Earnings Per Share - Schedule of Calculation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings per common share - basic:
Net income	$ 63,621	$ 50,473
Less: Preferred stock dividends	3,598	3,599
Less: Dividends and undistributed earnings allocated to unvested restricted shares	639	346
Net income allocated to common shareholders - basic	$ 59,384	$ 46,528
Weighted average common shares outstanding	53,616	46,123
Earnings per common share - basic (in usd per share)	$ 1.11	$ 1.01
Earnings per common share - diluted:
Net income allocated to common shareholders - basic	$ 59,384	$ 46,528
Adjustment for undistributed earnings allocated to unvested restricted shares	(18)	(37)
Earnings Allocated to Common Shareholders	$ 59,366	$ 46,491
Weighted average common shares outstanding	53,616	46,123
Dilutive potential common shares	351	373
Weighted average common shares outstanding - diluted	53,967	46,496
Earnings per common share - diluted (in usd per share)	$ 1.10	$ 1.00