Commitments and Contingencies - Additional Information (Detail) - USD ($)	1 Months Ended	6 Months Ended
	May 31, 2018	Jun. 30, 2019	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Remaining long-term lease commitments		$ 18,093,000
Commitments outstanding, aggregate amount		1,136,972,000
Commitments expected to be funded in 2019		558,493,000
Short-term borrowing facility, maximum capacity		100,000,000
Short-term borrowing facility, letters of credit		55,000,000
Letters of credit outstanding, amount		$ 4,006,000	$ 2,995,000
Short-term borrowing facility, expiration date		Oct. 31, 2019
FHLB stock purchased	$ 7,000,000.0
Fair value of collateral held at FHLB		$ 136,200,000
Total amount of guarantees outstanding		136,074,000
Life insurance policies with guarantees, cash value		$ 142,021,000