Commitments and Contingencies - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended
	May 31, 2018	Mar. 31, 2020
Financing Receivable, Impaired [Line Items]
Remaining long-term lease commitments		$ 13,767,000
Commitments outstanding, aggregate amount		1,279,058,000
Commitments expected to be funded in 2019		495,590,000
Short-term borrowing facility, maximum capacity		100,000,000
Short-term borrowing facility, letters of credit		55,000,000
Letters of credit outstanding, amount		$ 3,484,000
Short-term borrowing facility, expiration date		Oct. 31, 2020
FHLB stock purchased	$ 7,000,000.0
Total amount of guarantees outstanding		$ 121,379,000
Life insurance policies with guarantees, cash value		143,762,000
Collateralized Mortgage Obligations
Financing Receivable, Impaired [Line Items]
Fair value of collateral held at FHLB		112,700,000
Commercial Mortgage Loans
Financing Receivable, Impaired [Line Items]
Fair value of collateral held at FHLB		$ 1,500,000,000