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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings per common share - basic:
Net income	$ 75,124	$ 52,018	$ 138,745	$ 102,491
Less: Preferred stock dividends	949	949	4,547	4,548
Less: Dividends and undistributed earnings allocated to unvested restricted shares	767	361	1,409	707
Net income allocated to common shareholders - basic	$ 73,408	$ 50,708	$ 132,789	$ 97,236
Weighted average common shares outstanding	55,931	50,630	54,780	48,389
Earnings per common share - basic (in usd per share)	$ 1.31	$ 1.00	$ 2.42	$ 2.01
Earnings per common share - diluted:
Net income allocated to common shareholders - basic	$ 73,408	$ 50,708	$ 132,789	$ 97,236
Adjustment for undistributed earnings allocated to unvested restricted shares	(7)	(2)	(26)	(39)
Net income allocated to common shareholders - diluted	$ 73,401	$ 50,706	$ 132,763	$ 97,197
Weighted average common shares outstanding	55,931	50,630	54,780	48,389
Dilutive potential common shares	356	354	353	362
Weighted average common shares outstanding - diluted	56,287	50,984	55,133	48,751
Earnings per common share - diluted (in usd per share)	$ 1.30	$ 0.99	$ 2.41	$ 1.99