Investment Securities (Narrative) (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) security	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) security	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Investments, Debt and Equity Securities [Abstract]
Equity securities without readily determinable fair value	$ 31,100		$ 31,100
Upward adjustments of equity securities without readily determinable fair values	0	$ 110	393	$ 110
Downward adjustments of equity securities without readily determinable fair values	0	0	0	0
Impairment of equity securities without readily determinable fair values	388	263	2,085	263
Pledged securities	$ 3,200,000	$ 1,900,000	$ 3,200,000	$ 1,900,000	$ 1,700,000
Number of securities by a single non-government sponsored issuer exceeding 10% of shareholders' equity | security	0		0