Investment Securities - Additional Information (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) security	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) security	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Summary of Investment Holdings [Line Items]
Accrued interest receivable on available-for-sale debt securities excluded from estimate of credit losses	$ 26,400,000		$ 26,400,000
Other-than-temporary impairment loss				$ 0
Number of securities in security portfolio | security	1,842		1,842
Number of securities in unrealized loss position | security	68		68
Total investment securities - available-for-sale	$ 5,447,271,000		$ 5,447,271,000		$ 5,385,091,000
Unrealized losses	9,912,000		9,912,000		21,660,000
Equity securities, at fair value	40,246,000		40,246,000		6,842,000
Gains (losses) on equity securities	600,000	$ (18,000)	700,000	154,000
Impairments on equity securities without readily determinable fair value			0	0
Other assets
Summary of Investment Holdings [Line Items]
Equity securities without readily determinable fair value	$ 91,900,000		91,900,000		91,400,000
Pooled trust preferred securities
Summary of Investment Holdings [Line Items]
Other-than-temporary impairment loss			$ 0	$ 0
Number of pooled trust preferred securities | security	2		2
Total investment securities - available-for-sale	$ 7,185,000		$ 7,185,000		8,222,000
Unrealized losses	$ 6,600,000		$ 6,600,000		$ 5,589,000