Computation of Basic and Diluted Earnings per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Net Income (Loss) Available to Common Stockholders, Basic
Net income	$ 23,812	$ 16,155	$ 65,361	$ 41,379
Preferred stock dividends	0	863	0	2,569
Net income available to common stockholders	$ 23,812	$ 15,292	$ 65,361	$ 38,810
Weighted Average Number of Shares Outstanding, Basic and Diluted
Weighted average common shares outstanding for basic earnings per share computation	43,699,566	42,989,564	43,458,309	42,943,588
Dilutive effect of stock-based compensation	585,278	130,513	384,980	102,968
Weighted average common shares outstanding for diluted earnings per common share computation	44,284,844	43,120,077	43,843,289	43,046,556
Earnings Per Share, Basic and Diluted
Basic earnings per common share	$ 0.54	$ 0.36	$ 1.50	$ 0.90
Diluted earnings per common share	$ 0.54	$ 0.35	$ 1.49	$ 0.90
Stock Options
Earnings Per Share, Basic and Diluted [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount			875,714	2,814,277
Unvested Restricted Stock
Earnings Per Share, Basic and Diluted [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount			54,402	48,196