Investment Securities - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) Security	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) Security	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Summary Of Investment Holdings [Line Items]
Held-to-Maturity, Unrecognized Losses					$ 17,211,000
OTTI losses on securities			$ 0	$ 0
Number of securities in security portfolio | Security	1,937		1,937
Number of securities in unrealized loss position | Security	256		256
Total investment securities - available-for-sale	$ 4,916,979,000	$ 3,272,456,000	$ 4,916,979,000	3,272,456,000	4,123,416,000
Unrealized losses	13,573,000		13,573,000		70,573,000
Equity securities recorded at fair value	6,562,000	5,828,000	6,562,000	5,828,000	5,582,000
Gains on equity securities	200,000	$ 200,000	400,000	300,000
Impairments on equity securities without readily determinable fair value			0	0
Downward adjustments on equity securities without readily determinable fair value			0	0
Other Asstes [Member]
Summary Of Investment Holdings [Line Items]
Equity securities without readily determinable fair value	$ 93,300,000		$ 93,300,000		79,200,000
Pooled Trust Preferred Securities [Member]
Summary Of Investment Holdings [Line Items]
Number of pooled trust preferred securities | Security	2		2
Total investment securities - available-for-sale	$ 7,695,000		$ 7,695,000		8,495,000
Unrealized losses	6,130,000		6,130,000		5,366,000
OTTI losses on securities			0	$ 0
Held-to-maturity Securities [Member]
Summary Of Investment Holdings [Line Items]
Held-to-Maturity, Unrecognized Losses	$ 9,400,000		$ 9,400,000		$ 10,700,000