Investment Securities (Narrative) (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) security	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) security	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Investments, Debt and Equity Securities [Abstract]
Equity securities without readily determinable fair value	$ 30,000		$ 30,000
Upward adjustments of equity securities without readily determinable fair values	0	$ 0	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	0	0	2,085	263
Pledged securities	$ 3,000,000	$ 1,900,000	$ 3,000,000	$ 1,900,000	$ 1,700,000
Number of securities by a single non-government sponsored issuer exceeding 10% of shareholders' equity | security	0		0