Earnings Per Common Share - Computations of Diluted Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Earnings Per Share [Abstract]
Net income available to common equity	$ 315,714	$ 266,371	$ 593,924	$ 487,666
Less: Income attributable to unvested stock-based compensation awards	(2,740)	(2,890)	(5,217)	(5,353)
Net income available to common shareholders	$ 312,974	$ 263,481	$ 588,707	$ 482,313
Adjusted weighted-average shares outstanding:
Common and unvested stock-based compensation awards	159,164	133,818	159,692	133,680
Less: Unvested stock-based compensation awards	(1,362)	(1,462)	(1,424)	(1,477)
Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock	539	760	493	741
Adjusted weighted-average shares outstanding	158,341	133,116	158,761	132,944
Diluted earnings per common share	$ 1.98	$ 1.98	$ 3.71	$ 3.63