Earnings Per Common Share - Computations of Basic Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Income available to common shareholders:
Net income	$ 298,528	$ 241,613
Less: Preferred stock dividends	(20,318)	(20,318)
Net income available to common equity	278,210	221,295
Less: Income attributable to unvested stock-based compensation awards	(2,466)	(2,465)
Net income available to common shareholders	$ 275,744	$ 218,830
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards	160,220	133,542
Less: Unvested stock-based compensation awards	(1,486)	(1,493)
Weighted-average shares outstanding	158,734	132,049
Basic earnings per common share	$ 1.74	$ 1.66