Computation of Basic and Diluted Earnings per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Net Income (Loss) Available to Common Stockholders, Basic
Net income	$ 20,044	$ 12,214
Preferred stock dividends	0	853
Net income available to common stockholders	$ 20,044	$ 11,361
Weighted Average Number of Shares Outstanding, Basic and Diluted
Weighted average common shares outstanding for basic earnings per share computation	43,140,409	42,873,769
Dilutive effect of stock-based compensation	287,973	108,774
Weighted average common shares outstanding for diluted earnings per common share computation	43,428,382	42,982,543
Earnings Per Share, Basic and Diluted
Basic earnings per common share	$ 0.46	$ 0.26
Diluted earnings per common share	$ 0.46	$ 0.26
Stock Options
Earnings Per Share, Basic and Diluted [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1,025,419	2,657,668
Unvested Restricted Stock
Earnings Per Share, Basic and Diluted [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	61,760	48,196