|
Fair Value (Details) (Recurring basis, USD $)
In Thousands, unless otherwise specified |
Jun. 30, 2012
|
Dec. 31, 2011
|
|---|---|---|
|
Level 1
|
||
| Fair Value | ||
| Assets at Fair Value | $ 15,893 | $ 11,947 |
|
Level 1 | Money market funds
|
||
| Fair Value | ||
| Assets at Fair Value | 15,893 | 11,947 |
|
Level 2
|
||
| Fair Value | ||
| Assets at Fair Value | 185,437 | 235,007 |
|
Level 2 | U. S. treasury bills
|
||
| Fair Value | ||
| Assets at Fair Value | 3,002 | |
|
Level 2 | Government-sponsored enterprise securities
|
||
| Fair Value | ||
| Assets at Fair Value | 80,085 | 144,599 |
|
Level 2 | Corporate bonds and commercial paper
|
||
| Fair Value | ||
| Assets at Fair Value | 105,352 | 87,406 |
|
Total
|
||
| Fair Value | ||
| Assets at Fair Value | 201,330 | 246,954 |
|
Total | Money market funds
|
||
| Fair Value | ||
| Assets at Fair Value | 15,893 | 11,947 |
|
Total | U. S. treasury bills
|
||
| Fair Value | ||
| Assets at Fair Value | 3,002 | |
|
Total | Government-sponsored enterprise securities
|
||
| Fair Value | ||
| Assets at Fair Value | 80,085 | 144,599 |
|
Total | Corporate bonds and commercial paper
|
||
| Fair Value | ||
| Assets at Fair Value | $ 105,352 | $ 87,406 |