Investment Securities (Narrative) (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($) security	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) security	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Investments, Debt and Equity Securities [Abstract]
Equity securities without readily determinable fair value	$ 35,200		$ 35,200
Upward adjustments of equity securities without readily determinable fair values	0	$ 0	0	$ 393
Downward adjustments of equity securities without readily determinable fair values	0	0	0	0
Impairment of equity securities without readily determinable fair values	2,148	0	2,178	2,085
Pledged securities	$ 2,500,000	$ 3,000,000	$ 2,500,000	$ 3,000,000	$ 2,400,000
Number of securities by a single non-government sponsored issuer exceeding 10% of shareholders' equity | security	0		0