Earnings Per Share (Details) (USD $) In Thousands, except 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 per share:
Net income	$ 31,732	$ 48,074	$ 96,842	$ 162,845
Weighted average number of common shares outstanding	47,948,562	47,643,648	47,442,208	48,107,159
Basic net income per share	$ 0.66	$ 1.01	$ 2.04	$ 3.39
Diluted net income per share:
Net income	$ 31,732	$ 48,074	$ 96,842	$ 162,845
Weighted average number of common shares outstanding	47,948,562	47,643,648	47,442,208	48,107,159
Dilutive effect of stock options and non-vested stock awards	1,498,680	1,400,337	1,401,894	1,668,364
Dilutive effect of assumed conversion of the 2.0% Convertible Senior Notes	0	1,209,772	1,259,906	1,629,832
Dilutive effect of warrants	1,948,229	0	1,514,860	445,623
Weighted average number of common shares and dilutive potential common shares outstanding	51,395,471	50,253,757	51,618,868	51,850,978
Diluted net income per share	$ 0.62	$ 0.96	$ 1.88	$ 3.14
Earnings Per Share (Textual) [Abstract]
Antidilutive common stock shares		76,645		43,577