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, 2014	Dec. 31, 2013	Dec. 31, 2012
Net Income (Loss) Available to Common Stockholders, Basic [Abstract]
Net income	$ 84,401	$ 86,136	$ 58,224
Preferred stock dividends	0	0	3,300
Net income available to common shareholders	$ 84,401	$ 86,136	$ 54,924
Weighted Average Number of Shares Outstanding, Basic and Diluted [Abstract]
Weighted average common shares outstanding for basic earnings per share computation	44,615,060	43,566,681	42,965,987
Dilutive effect of stock-based compensation	595,501	477,921	126,991
Weighted average common shares outstanding for diluted earnings per common share computation	45,210,561	44,044,602	43,092,978
Earnings Per Share, Basic and Diluted [Abstract]
Basic earnings per common share (in dollars per share)	$ 1.89	$ 1.98	$ 1.28
Diluted earnings per common share (in dollars per share)	$ 1.87	$ 1.96	$ 1.27
Stock Options
Earnings Per Share, Basic and Diluted [Abstract]
Antidilutive securities excluded from computation of earnings per share (in shares)	5,000	21,372	2,427,823
Unvested Restricted Stock
Earnings Per Share, Basic and Diluted [Abstract]
Antidilutive securities excluded from computation of earnings per share (in shares)	88,797	37,734	41,240