Investment Securities (Schedule of Realized Gain (Loss)) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Realized gains on investment securities	$ 1,051	$ 58	$ 1,057	$ 106
Realized losses on investment securities	(50)	(19)	(1,051)	(75)
Net realized gains on investment securities	1,001	39	6	31
Unrealized gains on equity securities with readily determinable fair value	530	0	2,632	0
Unrealized losses on equity securities with readily determinable fair value	(1,111)	0	(2,176)	0
Net unrealized (losses) gains on equity securities with readily determinable fair value	(581)	0	456	0
Upward adjustments of equity securities without readily determinable fair values	0	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	(330)	0	(867)	0
Adjustment and impairment, net, of equity securities without readily determinable fair values	(330)	0	(711)	0
Other than temporary impairment charges	0	0	0	0
Gains (losses) on investment securities, net	90	39	(249)	31
Proceeds from sales of available-for-sale securities	649	133,089	209,640	121,795
Proceeds from sales of equity securities with readily determinable fair value	1,895	0	1,895	0
Proceeds from sales and capital distributions of equity securities without readily determinable fair value	$ 64	$ 0	$ 680	$ 0