Investment Securities (Narrative) (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) security	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) security	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Investments, Debt and Equity Securities [Abstract]
Equity securities with readily determinable fair value	$ 27,300		$ 27,300
Upward adjustments of equity securities without readily determinable fair values	110	$ 25	110	$ 156
Downward adjustments of equity securities without readily determinable fair values	0	0		0
Impairment of equity securities without readily determinable fair values	263	0	263	537
Pledged securities	$ 1,900,000	$ 1,700,000	$ 1,900,000	$ 1,700,000	$ 1,700,000
Number of securities by a single non-government sponsored issuer exceeding 10% of shareholders' equity | security	0		0