Net Income (Loss) Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Basic:
Net income (loss)	$ (8,757)	$ 22,331	$ (28,554)	$ 135,136
Basic	20,999	20,790	20,935	20,737
Net income (loss) per share	$ (0.42)	$ 1.07	$ (1.36)	$ 6.52
Diluted:
Net income (loss)	(8,757)	22,331	(28,554)	135,136
Interest on convertible senior debentures		1,391		4,353
Net income (loss) for dilutive share computation	$ (8,757)	$ 23,722	$ (28,554)	$ 139,489
Number of shares used in basic per share computation	20,999	20,790	20,935	20,737
Average common shares outstanding	20,999	24,291	20,935	24,573
Net income (loss) per share	$ (0.42)	$ 0.98	$ (1.36)	$ 5.68
Restricted Stock Option and Deferred Stock Unit [Member]
Diluted:
Unvested restricted stock and deferred stock units		46		68
Employee stock options [Member]
Diluted:
Unvested restricted stock and deferred stock units		600		707
Convertible Senior Debentures [Member]
Diluted:
Convertible senior debentures		2,855		3,061