Investment Securities (Schedule of Realized Gain (Loss)) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Realized gains on available-for-sale debt securities	$ 0	$ 0
Realized losses on available-for-sale debt securities	(975)	(55)
Net realized losses on available-for-sale debt securities	(975)	(55)
Unrealized gains on equity securities with readily determinable fair value	1,873	0
Unrealized losses on equity securities with readily determinable fair value	(843)	0
Net unrealized gains on equity securities with readily determinable fair value	1,030	0
Upward adjustments of equity securities without readily determinable fair values	131	0
Downward adjustments of equity securities without readily determinable fair values	0	0
Impairment of equity securities without readily determinable fair values	(537)	0
Adjustment and impairment, net, of equity securities without readily determinable fair values	(406)	0
Other than temporary impairment charges	0	0
Losses on investment securities, net	(351)	(55)
Proceeds from sales and calls of available-for-sale securities	210,891	6,005
Proceeds from calls of held-to-maturity securities	4,141	51,060
Proceeds from sales of equity securities with readily determinable fair value	0	0
Proceeds from sales of equity securities without readily determinable fair value	$ 0	$ 0