Investment Securities (Schedule of Realized Gain (Loss)) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Realized gains	$ 58	$ 3,429	$ 106	$ 7,466
Realized losses	(19)	(124)	(75)	(1,396)
Net realized gains	39	3,305	31	6,070
Other than temporary impairment charges	0	0	0	0
Gains on investment securities, net	39	3,305	31	6,070
Proceeds from sales and calls of available-for-sale securities	136,789	1,114,666	146,518	2,186,662
Proceeds from calls of held-to-maturity securities	$ 17	$ 141,885	$ 51,079	$ 423,866