Computation of Basic and Diluted Earnings per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Net Income (Loss) Available to Common Stockholders, Basic
Net income	$ 13,010	$ 9,854	$ 25,224	$ 19,360
Preferred stock dividends	853	853	1,706	1,697
Net income available to common stockholders	$ 12,157	$ 9,001	$ 23,518	$ 17,663
Weighted Average Number of Shares Outstanding, Basic and Diluted
Weighted average common shares outstanding for basic earnings per share computation	42,966,926	42,781,894	42,920,347	42,735,897
Dilutive effect of stock-based compensation	93,278	114,717	96,111	138,031
Weighted average common shares outstanding for diluted earnings per common share computation	43,060,204	42,896,611	43,016,458	42,873,928
Earnings Per Share, Basic and Diluted
Basic earnings per common share	$ 0.28	$ 0.21	$ 0.55	$ 0.41
Diluted earnings per common share	$ 0.28	$ 0.21	$ 0.55	$ 0.41
Stock Options
Earnings Per Share, Basic and Diluted [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount			2,828,234	2,623,276
Unvested Restricted Stock
Earnings Per Share, Basic and Diluted [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount			48,196	33,068