| Cash, Cash Equivalents and Available-For-Sale Securities (Tables)
 | 9 Months Ended | 
      
        | Sep. 30, 2014 | 
      
        | CASH, CASH EQUIVALENTS AND AVAILABLE-FOR-SALE SECURITIES |  | 
      
        | Schedule of cash, cash equivalents and available-for-sale securities |  
		
			Cash, cash equivalents and available-for-sale securities consisted of the following (in thousands):
		 
			 
		 
			
				| 
						  | 
						  | 
						September 30, | 
						  | 
						December 31, | 
						  |  
				| 
						  | 
						  | 
						2014 | 
						  | 
						2013 | 
						  |  
				| 
						Checking account  | 
						  | 
						$ | 760 | 
						  | 
						$ | 195 | 
						  |  
				| 
						Money market funds | 
						  | 8,754 | 
						  | 9,059 | 
						  |  
				| 
						U. S. treasury bills | 
						  | 2,029 | 
						  | 2,085 | 
						  |  
				| 
						Government-sponsored enterprise securities | 
						  | 52,093 | 
						  | 67,178 | 
						  |  
				| 
						Corporate bonds and commercial paper | 
						  | 94,036 | 
						  | 133,458 | 
						  |  
				| 
						  | 
						  | 
						  | 
						  | 
						  | 
						  |  
				| 
						  | 
						  | 
						$ | 157,672 | 
						  | 
						$ | 211,975 | 
						  |  
				| 
						  | 
						  | 
						  | 
						  | 
						  | 
						  |  
				| 
						Reported as:  | 
						  | 
						  | 
						  | 
						  | 
						  |  
				| 
						Cash and cash equivalents  | 
						  | 
						$ | 12,814 | 
						  | 
						$ | 20,854 | 
						  |  
				| 
						Available-for-sale securities  | 
						  | 144,858 | 
						  | 191,121 | 
						  |  
				| 
						  | 
						  | 
						  | 
						  | 
						  | 
						  |  
				| 
						  | 
						  | 
						$ | 157,672 | 
						  | 
						$ | 211,975 | 
						  | 
			 
		   | 
      
        | Schedule of cash equivalents and available-for-sale securities including the securities with unrealized gains and losses |  
		
			Cash equivalents and available-for-sale securities include the following securities with unrealized gains and losses (in thousands):
		 
			 
		 
			
				| 
						  | 
						  | 
						  | 
						  | 
						Gross | 
						  | 
						Gross | 
						  | 
						  | 
						  |  
				| 
						  | 
						  | 
						Amortized | 
						  | 
						Unrealized | 
						  | 
						Unrealized | 
						  | 
						  | 
						  |  
				| 
						September 30, 2014 | 
						  | 
						Cost | 
						  | 
						Gains | 
						  | 
						Losses | 
						  | 
						Fair Value | 
						  |  
				| 
						U. S. treasury bills | 
						  | 
						$ | 2,027 | 
						  | 
						$ | 2 | 
						  | 
						$ | 
						— | 
						  | 
						$ | 2,029 | 
						  |  
				| 
						Government-sponsored enterprise securities | 
						  | 52,082 | 
						  | 19 | 
						  | (8 | 
						) | 52,093 | 
						  |  
				| 
						Corporate bonds and commercial paper | 
						  | 94,033 | 
						  | 21 | 
						  | (18 | 
						) | 94,036 | 
						  |  
				| 
						  | 
						  | 
						  | 
						  | 
						  | 
						  | 
						  | 
						  | 
						  | 
						  |  
				| 
						Total  | 
						  | 
						$ | 148,142 | 
						  | 
						$ | 42 | 
						  | 
						$ | (26 | 
						) | 
						$ | 148,158 | 
						  | 
			 
		 
			
				| 
						  | 
						  | 
						  | 
						  | 
						Gross | 
						  | 
						Gross | 
						  | 
						  | 
						  |  
				| 
						  | 
						  | 
						Amortized | 
						  | 
						Unrealized | 
						  | 
						Unrealized | 
						  | 
						  | 
						  |  
				| 
						December 31, 2013 | 
						  | 
						Cost | 
						  | 
						Gains | 
						  | 
						Losses | 
						  | 
						Fair Value | 
						  |  
				| 
						U. S. treasury bills | 
						  | 
						$ | 2,083 | 
						  | 
						$ | 2 | 
						  | 
						$ | 
						— | 
						  | 
						$ | 2,085 | 
						  |  
				| 
						Government-sponsored enterprise securities | 
						  | 67,160 | 
						  | 29 | 
						  | (11 | 
						) | 67,178 | 
						  |  
				| 
						Corporate bonds and commercial paper | 
						  | 133,431 | 
						  | 33 | 
						  | (6 | 
						) | 133,458 | 
						  |  
				| 
						  | 
						  | 
						  | 
						  | 
						  | 
						  | 
						  | 
						  | 
						  | 
						  |  
				| 
						Total  | 
						  | 
						$ | 202,674 | 
						  | 
						$ | 64 | 
						  | 
						$ | (17 | 
						) | 
						$ | 202,721 | 
						  | 
			 
		   | 
      
        | Schedule of contractual maturities of cash equivalents and available-for-sale securities |  
		
			As of September 30, 2014, the contractual maturities of our cash equivalents and available-for-sale securities were (in thousands):
		 
			 
		 
			
				| 
						  | 
						  | 
						Years to Maturity | 
						  |  
				| 
						  | 
						  | 
						  | 
						  | 
						After One Year | 
						  |  
				| 
						  | 
						  | 
						Within One | 
						  | 
						Through | 
						  |  
				| 
						  | 
						  | 
						Year | 
						  | 
						Two Years | 
						  |  
				| 
						U. S. treasury bills | 
						  | 
						$ | 2,029 | 
						  | 
						$ | 
						— | 
						  |  
				| 
						Government-sponsored enterprise securities | 
						  | 32,523 | 
						  | 19,570 | 
						  |  
				| 
						Corporate bonds and commercial paper | 
						  | 88,514 | 
						  | 5,522 | 
						  |  
				| 
						Total  | 
						  | 
						$ | 123,066 | 
						  | 
						$ | 25,092 | 
						  | 
			 
		   | 
      
        | Schedule of fair value and gross unrealized losses of the entity's investments in unrealized loss position |  
		
			The following table shows the fair value and gross unrealized losses of our investments in individual securities that are in an unrealized loss position, aggregated by investment category (in thousands):
		 
			 
		 
			
				| 
						  | 
						  | 
						  | 
						  | 
						Unrealized | 
						  |  
				| 
						September 30, 2014 | 
						  | 
						Fair Value | 
						  | 
						Losses | 
						  |  
				| 
						Government-sponsored enterprise securities | 
						  | 
						$ | 14,804 | 
						  | 
						$ | (8 | 
						) |  
				| 
						Corporate bonds and commercial paper | 
						  | 27,289 | 
						  | (18 | 
						) |  
				| 
						Total  | 
						  | 
						$ | 42,093 | 
						  | 
						$ | (26 | 
						) | 
			 
		   |