Other Borrowings - Additional Information (Detail)	Dec. 31, 2020 USD ($)
Debt Disclosure [Abstract]
Repurchase investment securities sold and pledged as collateral under securities repurchase agreement	$ 49,211,000
FHLB collateral line of credit, maximum borrowings capacity	1,932,399,000
FHLB collateral line of credit, outstanding balance	0
Loans designated as potential collateral under collateralized line of credit with FHLB	112,456,000
Investment securities designated as potential collateral under collateral line of credit	3,205,959,000
Collateralized line of credit with San Francisco Federal Reserve Bank, maximum borrowings capacity	157,884,000
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	8,100
Loans designated as potential collateral under collateral line of credit with San Francisco Federal Reserve Bank	328,011,000
Unused correspondent banking lines of credit from commercial banks for federal funds	$ 60,000,000