Earnings per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Basic EPS:
Net income (loss)	$ 21,886	$ 22,997	$ 19,280	$ 15,854	$ 14,770	$ 8,234	$ 10,840	$ 7,782	$ 80,017	$ 41,626	$ (20,573)
Weighted average number of common shares outstanding									90,022	89,103	88,500
Basic income (loss) per common share	$ 0.24	$ 0.25	$ 0.21	$ 0.18	$ 0.16	$ 0.09	$ 0.12	$ 0.09	$ 0.89	$ 0.47	$ (0.23)
Diluted EPS:
Net income (loss)	21,886	22,997	19,280	15,854	14,770	8,234	10,840	7,782	80,017	41,626	(20,573)
Assumed conversions of Senior Notes									4,969	1,138
Adjusted net income (loss)									$ 84,986	$ 42,764	$ (20,573)
Weighted average number of common shares outstanding									90,022	89,103	88,500
Add: Dilutive effect of stock options and restricted stock awards									965	790
Dilutive effect of Senior Notes									15,682	3,824
Diluted weighted average number of common shares outstanding									106,669	93,717	88,500
Diluted income (loss) per common share	$ 0.22	$ 0.23	$ 0.19	$ 0.16	$ 0.15	$ 0.09	$ 0.12	$ 0.09	$ 0.80	$ 0.46	$ (0.23)
Stock options and warrants excluded from calculation of diluted earnings per share because anti-dilutive for the period									2,907	3,913	6,613