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, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Net Income (Loss) Available to Common Stockholders, Basic
Net income	$ 21,505	$ 13,010	$ 41,549	$ 25,224
Preferred stock dividends	0	853	0	1,706
Net income available to common stockholders	$ 21,505	$ 12,157	$ 41,549	$ 23,518
Weighted Average Number of Shares Outstanding, Basic and Diluted
Weighted average common shares outstanding for basic earnings per share computation	43,480,502	42,966,926	43,335,682	42,920,347
Dilutive effect of stock-based compensation	427,785	93,278	376,978	96,111
Weighted average common shares outstanding for diluted earnings per common share computation	43,908,287	43,060,204	43,712,660	43,016,458
Earnings Per Share, Basic and Diluted
Basic earnings per common share	$ 0.49	$ 0.28	$ 0.96	$ 0.55
Diluted earnings per common share	$ 0.49	$ 0.28	$ 0.95	$ 0.55
Stock Options
Earnings Per Share, Basic and Diluted [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount			976,063	2,828,234
Unvested Restricted Stock
Earnings Per Share, Basic and Diluted [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount			56,668	48,196