Investments - Other Investments - Additional Information (Detail)	Dec. 31, 2019 USD ($) Investment Venture	Dec. 31, 2018 USD ($)
Schedule of Equity Method Investments [Line Items]
Assets	$ 40,000,000.0	$ 59,500,000
Non controlling interest certified low-income housing developments | Investment	8
Other Investments [Member]
Schedule of Equity Method Investments [Line Items]
Assets	$ 4,500,000	$ 5,000,000.0
Other Investments [Member] | Four Venture Capital Funds [Member]
Schedule of Equity Method Investments [Line Items]
Assets	$ 4,500,000
Non controlling interest in venture capital funds number | Venture	4
Other Investments [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Schedule of Equity Method Investments [Line Items]
Assets	$ 5,300,000
Liabilities	400,000
Other Investments [Member] | Variable Interest Entity, Not Primary Beneficiary [Member] | Eight Certified Low Income Housing Developments [Member]
Schedule of Equity Method Investments [Line Items]
Carrying value of investments	$ 0