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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings per common share - basic:
Net income	$ 52,018	$ 50,810	$ 102,491	$ 93,579
Preferred stock dividends	(949)	(854)	(4,548)	(3,430)
Dividends and undistributed earnings allocated to unvested restricted shares	(361)	(540)	(707)	(1,003)
Net income allocated to common shareholders - basic	$ 50,708	$ 49,416	$ 97,236	$ 89,146
Weighted average common shares outstanding	50,630	40,771	48,389	40,741
Earnings per common share - basic (in usd per share)	$ 1.00	$ 1.21	$ 2.01	$ 2.19
Earnings per common share - diluted:
Net income allocated to common shareholders - basic	$ 50,708	$ 49,416	$ 97,236	$ 89,146
Dividends and undistributed earnings allocated to unvested restricted shares	(2)	(12)	(39)	(13)
Earnings Allocated to Common Shareholders	$ 50,706	$ 49,404	$ 97,197	$ 89,133
Weighted average common shares outstanding	50,630	40,771	48,389	40,741
Dilutive potential common shares	354	137	362	86
Weighted average common shares outstanding - diluted	50,984	40,908	48,751	40,827
Earnings per common share - diluted (in usd per share)	$ 0.99	$ 1.21	$ 1.99	$ 2.18