Earnings per Share (Details) (USD $) In Thousands, except Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Schedule of Earnings per Share Basic and Diluted [Line Items]
Net income	$ 72,614	$ 21,205	$ 108,295	$ 46,063
Weighted average common shares outstanding, basic	53,534,000	52,991,000	53,414,000	52,773,000
Plus: net effect of dilutive stock options and restricted common shares	726,000	368,000	828,000	232,000
Weighted average common shares outstanding, diluted	54,260,000	53,359,000	54,242,000	53,005,000
Earnings per share, basic	$ 1.36	$ 0.40	$ 2.03	$ 0.87
Earnings per share, diluted	$ 1.34	$ 0.40	$ 2.00	$ 0.87
Antidilutive Common Stock Shares Excluded from Computation of Earnings Per Share	7,618,529	7,150,519	7,351,738	8,684,283
Restricted Stock [Member]
Schedule of Earnings per Share Basic and Diluted [Line Items]
Antidilutive Common Stock Shares Excluded from Computation of Earnings Per Share	0	6,750	83,297	8,500