(Loss) Earnings Per Common 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
Numerator [Abstract]
Net (loss) income	$ (2,017)	$ 61,949	$ 83,324	$ 163,293
Denominator [Abstract]
Denominator for basic earnings per common share-weighted average shares (in shares)	59,558	66,655	62,087	67,722
Effect of dilutive securities [Abstract]
Employee stock-based compensation (in shares)	0	1,916	1,537	2,125
Denominator for diluted earnings per common share-adjusted weighted average shares (in shares)	59,558	68,571	63,624	69,847
Basic earnings per common share (in dollars per share)	$ (0.03)	$ 0.93	$ 1.34	$ 2.41
Diluted earnings per common share (in dollars per share)	$ (0.03)	$ 0.90	$ 1.31	$ 2.34
Shares excluded from diluted earnings per common share computation as anti-dilutive (in shares)		8	103	4