Earnings per Share (Details) (USD $) In Thousands, except Share data	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Schedule of Earnings per Share Basic and Diluted [Line Items]
Net income	$ 11,440	$ 15,426	$ 35,681	$ 24,858
Weighted average common shares outstanding, basic	53,441,000	52,819,000	53,343,000	52,658,000
Plus: net effect of dilutive stock options and restricted common shares	873,000	105,000	880,000	165,000
Weighted average common shares outstanding, diluted	54,314,000	52,924,000	54,223,000	52,823,000
Earnings per share, basic	$ 0.21	$ 0.29	$ 0.67	$ 0.47
Earnings per share, diluted	$ 0.21	$ 0.29	$ 0.66	$ 0.47
Antidilutive Common Stock Shares Excluded from Computation of Earnings Per Share	7,078,216	9,046,877	7,218,343	9,451,165
Restricted Stock [Member]
Schedule of Earnings per Share Basic and Diluted [Line Items]
Antidilutive Common Stock Shares Excluded from Computation of Earnings Per Share	47,312	18,750	124,946	9,735