Investments in Limited Partnerships - Additional Information (Detail) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) Partnership	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Schedule of Investments [Line Items]
Tax benefits including low-income housing and historic tax credits	$ 7,046	$ 8,334	$ 10,103	$ 8,858	$ 10,556	$ 6,516	$ 7,335	$ 7,004	$ 34,341	$ 31,412	$ 53,807
Partnerships losses and impairment									$ 2,600	2,100	1,500
Number of limited partnerships held | Partnership									8
Equity Method Investments [Member] | Accounting Standards Update 2014-01 [Member]
Schedule of Investments [Line Items]
Tax benefits including low-income housing and historic tax credits									$ 2,500	2,100	1,600
Other Liabilities [Member]
Schedule of Investments [Line Items]
Unfunded equity commitments in other liabilities	15,600				13,000				15,600	13,000
Limited Liability Company [Member]
Schedule of Investments [Line Items]
Amount invested in partnerships	7,100				6,600				7,100	6,600
Partnership gains (losses) under equity method									618	712	$ 47
Variable Interest Entity, Not Primary Beneficiary [Member] | Other Assets [Member]
Schedule of Investments [Line Items]
Amount invested in partnerships	$ 25,700				$ 21,300				$ 25,700	$ 21,300