Investment Securities - Additional Information (Detail)	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 ($)
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	1,995		1,995
Number of securities in unrealized loss position | Security	287		287
Total investment securities - available-for-sale	$ 4,667,226,000	$ 3,181,665,000	$ 4,667,226,000	3,181,665,000	4,123,416,000
Unrealized losses	16,168,000		16,168,000		70,573,000
Securities portfolio at fair value	6,234,000	5,596,000	6,234,000	5,596,000	5,582,000
Gains (losses) on equity securities	(18,000)	$ 12,000	154,000	97,000
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	$ 84,900,000		$ 84,900,000		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	$ 7,836,000		$ 7,836,000		8,495,000
Unrealized losses	$ 6,000,000		6,000,000		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					$ 10,700,000