Investment Securities (Schedule of Realized Gain (Loss)) (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Realized gains on investment securities	$ 17,000	$ 0
Realized losses on investment securities	(84,000)	(975,000)
Net realized losses on investment securities	(67,000)	(975,000)
Unrealized gains on equity securities with readily determinable fair value	1,431,000	1,873,000
Unrealized losses on equity securities with readily determinable fair value	0	(843,000)
Net unrealized gains on equity securities with readily determinable fair value	1,431,000	1,030,000
Upward adjustments of equity securities without readily determinable fair values	0	131,000
Downward adjustments of equity securities without readily determinable fair values	0	0
Impairment of equity securities without readily determinable fair values	0	(537,000)
Adjustment and impairment, net, of equity securities without readily determinable fair values	0	(406,000)
Other than temporary impairment charges	0	0
Gains (losses) on investment securities, net	1,364,000	(351,000)
Proceeds from sales of available-for-sale securities	263,456,000	210,891,000
Proceeds from sales of equity securities with readily determinable fair value	0	0
Proceeds from sales and capital distributions of equity securities without readily determinable fair value	$ 220,000	$ 0