Income Taxes - Schedule of Income Taxes Expenses Benefit Reconciliation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income taxes at statutory federal income tax rate	$ 813,352	$ 720,439	$ 586,142
Increase (decrease) in taxes:
Tax-exempt income	(40,778)	(35,364)	(33,102)
State and local income taxes, net of federal income tax effect	83,327	79,155	60,988
Qualified affordable housing project federal tax credits, net	(16,015)	(15,091)	(15,297)
Initial impact of enactment of Tax Act	85,431
Other	(9,761)	(5,855)	(3,706)
Income taxes	$ 915,556	$ 743,284	$ 595,025