Net Income (Loss) Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Net Income (Loss) Per Common Share
Number of outstanding options not included in computation of Diluted EPS (in shares)	3,279,000	3,298,000	3,112,000	3,368,000
Numerator
Net Income (loss)	$ (14,737)	$ 20,720	$ (37,624)	$ 23,955
Denominator
Weighted average number of common shares outstanding	51,183,000	51,881,000	51,310,000	51,822,000
Effect of outstanding share-based awards (in shares)		666,000		700,000
Weighted average number of shares for diluted net income per common share	51,183,000	52,547,000	51,310,000	52,522,000
Basic earnings (loss) per share (in dollars per share)	$ (0.29)	$ 0.40	$ (0.73)	$ 0.46
Diluted earnings (loss) per share (in dollars per share)	$ (0.29)	$ 0.39	$ (0.73)	$ 0.46