Comprehensive Income (Details) (USD $) In Thousands | 3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2011 | Sep. 30, 2010 | Sep. 30, 2011 | Sep. 30, 2010 | |
| Comprehensive Income [Abstract] | ||||
| Net income | $ 16,473 | $ 10,629 | $ 50,024 | $ 26,242 |
| Unrealized gain (loss) on investments | 250 | 1,100 | (250) | |
| Defined benefit plans, net of tax | (958) | 412 | (1,085) | 131 |
| Total comprehensive income | $ 15,515 | $ 11,291 | $ 50,039 | $ 26,123 |