Other Borrowings - Additional Information (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Borrowings [Line Items]
FHLB collateral line of credit, maximum borrowings capacity	$ 2,257,336,000
FHLB collateral line of credit, outstanding balance	0
Loans designated as potential collateral under collateralized line of credit with FHLB	160,134,000
Investment securities designated as potential collateral under collateral line of credit	3,070,793,000
Repurchase investment securities sold and pledged as collateral under securities repurchase agreement	48,878,000
Collateralized line of credit with San Francisco Federal Reserve Bank, maximum borrowings capacity	273,395,000
Collateralized line of credit with San Francisco Federal Reserve Bank, outstanding balance	0
Investment securities designated as potential collateral under collateral line of credit with San Francisco Federal Reserve Bank	10,000
Loans designated as potential collateral under collateral line of credit with San Francisco Federal Reserve Bank	273,385,000
Unused correspondent banking lines of credit from commercial banks for federal funds	60,000,000
0.05% Fixed Rate Collateralized Borrowings
Schedule Of Borrowings [Line Items]
Other collateralized borrowings	$ 18,454,000	$ 15,839,000