Investment Securities (Schedule of Realized Gain (Loss)) (Detail) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Realized gains on investment debt securities	$ 6		$ 48	$ 6	$ 48
Realized losses on investment debt securities	(26)		(1)	(1,001)	(56)
Net realized (losses) gains on investment debt securities	(20)		47	(995)	(8)
Unrealized gains on equity securities with readily determinable fair value	229		0	2,102	0
Unrealized losses on equity securities with readily determinable fair value	(222)		0	(1,065)	0
Net unrealized gains on equity securities with readily determinable fair value	7	$ 1,000	0	1,037	0
Upward adjustments of equity securities without readily determinable fair values	25		0	156	0
Downward adjustments of equity securities without readily determinable fair values	0		0	0	0
Impairment of equity securities without readily determinable fair values	0		0	(537)	0
Adjustment and impairment, net, of equity securities without readily determinable fair values	25		0	(381)	0
Other than temporary impairment charges	0		0	0	0
Gains (losses) on investment securities, net	12		47	(339)	(8)
Proceeds from sales of available-for-sale securities	0		0	208,991	3,676
Proceeds from sales of equity securities with readily determinable fair value	0		0	0	0
Proceeds from sales and capital distributions of equity securities without readily determinable fair value	$ 616		$ 0	$ 616	$ 0