Net Income (Loss) Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Basic EPS
Net income (loss) available to common stockholders	$ (581,528)	$ (46,265)	$ (35,040)	$ 12,270	$ 37,550	$ (15,821)	$ 22,973	$ 3,975	$ (650,563)	$ 48,677	$ 93,499
Weighted average shares
Basic (in shares)									97,864,000	89,437,000	89,383,000
Effect of share based compensation plans (in shares)									0	166,000	342,000
Diluted (in shares)									97,864,000	89,603,000	89,725,000
Income (loss) per share
Basic (in dollars per share)	$ (5.77)	$ (0.46)	$ (0.35)	$ 0.14	$ 0.42	$ (0.18)	$ 0.26	$ 0.04	$ (6.65)	$ 0.54	$ 1.05
Diluted (in dollars per share)	$ (5.77)	$ (0.46)	$ (0.35)	$ 0.14	$ 0.42	$ (0.18)	$ 0.26	$ 0.04	$ (6.65)	$ 0.54	$ 1.04
Convertible Senior Notes Due March 2028 [Member]
Earnings Per Share (Textual) [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	3.25%				3.25%				3.25%	3.25%
Stock Options [Member]
Earnings Per Share (Textual) [Abstract]
Number of shares of common stock equivalents related to convertible debt									1,111,021	479,767	4,258
Convertible Debt [Member]
Earnings Per Share (Textual) [Abstract]
Number of shares of common stock equivalents related to convertible debt											1,059,228