Investment Securities (Schedule of Realized Gain (Loss)) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Realized gains	$ 48	$ 1,487	$ 48	$ 4,037
Realized losses	(1)	(47)	(56)	(1,272)
Net realized gains (losses)	47	1,440	(8)	2,765
Other than temporary impairment charges	0	0	0	0
Gains (losses) on investment securities, net	47	1,440	(8)	2,765
Proceeds from sales and calls of available-for-sale securities	3,724	1,068,795	9,729	1,071,996
Proceeds from calls of held-to-maturity securities	$ 2	$ 183,738	$ 51,062	$ 281,981