Securities (Sales of Securities Available for Sale) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Proceeds from sales	$ 14,847,380	$ 12,683,169	$ 12,151,287
Gross realized gains	13,289	228	39
Gross realized losses	(2,059)	(159)	(1)
Tax expense related to securities gains/losses	$ (3,931)	$ (24)	$ (13)