Earnings per Common Share Computation of Basic and Diluted Earnings per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net Income (Loss) Available to Common Stockholders, Basic [Abstract]
Net income	$ 58,224	$ 44,546	$ 37,356
Preferred stock dividends	3,300	3,422	3,422
Net income available to common shareholders	$ 54,924	$ 41,124	$ 33,934
Weighted Average Number of Shares Outstanding, Basic and Diluted [Abstract]
Weighted average common shares outstanding for basic earnings per share computation	42,965,987	42,749,526	39,907,640
Dilutive effect of stock-based compensation	126,991	97,670	219,725
Weighted average common shares outstanding for diluted earnings per common share computation	43,092,978	42,847,196	40,127,365
Earnings Per Share, Basic and Diluted [Abstract]
Basic earnings per common share (in dollars per share)	$ 1.28	$ 0.96	$ 0.85
Diluted earnings per common share (in dollars per share)	$ 1.27	$ 0.96	$ 0.85
Stock Options
Earnings Per Share, Basic and Diluted [Abstract]
Antidilutive securities excluded from computation of earnings per share (in shares)	2,427,823	2,865,832	2,301,413
Unvested Restricted Stock
Earnings Per Share, Basic and Diluted [Abstract]
Antidilutive securities excluded from computation of earnings per share (in shares)	41,240	9,427	17,644