|
Fair Value (Details) (Recurring basis, USD $)
In Thousands, unless otherwise specified |
Mar. 31, 2014
|
Dec. 31, 2013
|
|---|---|---|
|
Level 1
|
||
| Fair Value | ||
| Investments at fair value | $ 13,625 | $ 9,059 |
|
Level 1 | Money market funds
|
||
| Fair Value | ||
| Investments at fair value | 13,625 | 9,059 |
|
Level 2
|
||
| Fair Value | ||
| Investments at fair value | 181,350 | 202,721 |
|
Level 2 | U. S. treasury bills
|
||
| Fair Value | ||
| Investments at fair value | 2,068 | 2,085 |
|
Level 2 | Government-sponsored enterprise securities
|
||
| Fair Value | ||
| Investments at fair value | 62,827 | 67,178 |
|
Level 2 | Corporate bonds and commercial paper
|
||
| Fair Value | ||
| Investments at fair value | 116,455 | 133,458 |
|
Total
|
||
| Fair Value | ||
| Investments at fair value | 194,975 | 211,780 |
|
Total | Money market funds
|
||
| Fair Value | ||
| Investments at fair value | 13,625 | 9,059 |
|
Total | U. S. treasury bills
|
||
| Fair Value | ||
| Investments at fair value | 2,068 | 2,085 |
|
Total | Government-sponsored enterprise securities
|
||
| Fair Value | ||
| Investments at fair value | 62,827 | 67,178 |
|
Total | Corporate bonds and commercial paper
|
||
| Fair Value | ||
| Investments at fair value | $ 116,455 | $ 133,458 |