|
Fair Value (Details) (Recurring basis, USD $)
In Thousands, unless otherwise specified |
Sep. 30, 2012
|
Dec. 31, 2011
|
|---|---|---|
|
Level 1
|
||
| Fair Value | ||
| Investments at Fair Value | $ 9,198 | $ 11,947 |
|
Level 1 | Money market funds
|
||
| Fair Value | ||
| Investments at Fair Value | 9,198 | 11,947 |
|
Level 2
|
||
| Fair Value | ||
| Investments at Fair Value | 174,581 | 235,007 |
|
Level 2 | U. S. treasury bills
|
||
| Fair Value | ||
| Investments at Fair Value | 3,002 | |
|
Level 2 | Government-sponsored enterprise securities
|
||
| Fair Value | ||
| Investments at Fair Value | 50,902 | 144,599 |
|
Level 2 | Corporate bonds and commercial paper
|
||
| Fair Value | ||
| Investments at Fair Value | 123,679 | 87,406 |
|
Total
|
||
| Fair Value | ||
| Investments at Fair Value | 183,779 | 246,954 |
|
Total | Money market funds
|
||
| Fair Value | ||
| Investments at Fair Value | 9,198 | 11,947 |
|
Total | U. S. treasury bills
|
||
| Fair Value | ||
| Investments at Fair Value | 3,002 | |
|
Total | Government-sponsored enterprise securities
|
||
| Fair Value | ||
| Investments at Fair Value | 50,902 | 144,599 |
|
Total | Corporate bonds and commercial paper
|
||
| Fair Value | ||
| Investments at Fair Value | $ 123,679 | $ 87,406 |