Investment Securities - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2020 USD ($) security	Mar. 31, 2019 USD ($)	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	$ 22,600,000
Other-than-temporary impairment loss		$ 0
Number of securities in security portfolio | security	1,867
Number of securities in unrealized loss position | security	186
Total investment securities - available-for-sale	$ 5,360,025,000		$ 5,385,091,000
Unrealized losses	12,698,000		21,660,000
Equity securities	6,870,000		6,842,000
Gains on equity securities	100,000	200,000
Impairments on equity securities without readily determinable fair value	0	0
Other Asstes
Summary of Investment Holdings [Line Items]
Equity securities without readily determinable fair value	93,100,000		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
Total investment securities - available-for-sale	$ 7,422,000		8,222,000
Unrealized losses	$ 6,376,000		$ 5,589,000