|
Fair Value (Details) (Recurring basis, USD $)
In Thousands, unless otherwise specified |
Sep. 30, 2013
|
Dec. 31, 2012
|
|---|---|---|
|
Level 1
|
||
| Fair Value | ||
| Investments at fair value | $ 14,437 | $ 23,936 |
|
Level 1 | Money market funds
|
||
| Fair Value | ||
| Investments at fair value | 14,437 | 23,936 |
|
Level 2
|
||
| Fair Value | ||
| Investments at fair value | 216,351 | 274,054 |
|
Level 2 | U. S. treasury bills
|
||
| Fair Value | ||
| Investments at fair value | 2,104 | |
|
Level 2 | Government-sponsored enterprise securities
|
||
| Fair Value | ||
| Investments at fair value | 80,867 | 77,047 |
|
Level 2 | Corporate bonds and commercial paper
|
||
| Fair Value | ||
| Investments at fair value | 133,380 | 197,007 |
|
Total
|
||
| Fair Value | ||
| Investments at fair value | 230,788 | 297,990 |
|
Total | Money market funds
|
||
| Fair Value | ||
| Investments at fair value | 14,437 | 23,936 |
|
Total | U. S. treasury bills
|
||
| Fair Value | ||
| Investments at fair value | 2,104 | |
|
Total | Government-sponsored enterprise securities
|
||
| Fair Value | ||
| Investments at fair value | 80,867 | 77,047 |
|
Total | Corporate bonds and commercial paper
|
||
| Fair Value | ||
| Investments at fair value | $ 133,380 | $ 197,007 |