Other Borrowings - Additional Information (Detail) - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Debt Disclosure [Abstract]
Security repurchase agreement	$ 0	$ 0
Other collateralized borrowings	19,235,000	$ 12,328,000
Repurchase investment securities sold and pledged as collateral under securities repurchase agreement	21,022,000
FHLB collateral line of credit, maximum borrowings capacity	1,266,202,000
FHLB collateral line of credit, outstanding balance	0
FHLB collateral line of credit, remaining borrowing capacity	1,266,202,000
Loans designated as potential collateral under collateralized line of credit with FHLB	85,944,000
Investment securities designated as potential collateral under collateral line of credit	1,819,129,000
Collateralized line of credit with San Francisco Federal Reserve Bank, maximum borrowings capacity	115,435,000
Collateralized line of credit with San Francisco Federal Reserve Bank, outstanding balance	0
Collateralized line of credit with San Francisco Federal Reserve Bank, remaining borrowing capacity	115,435,000
Investment securities designated as potential collateral under collateral line of credit with San Francisco Federal Reserve Bank	216,000
Loans designated as potential collateral under collateral line of credit with San Francisco Federal Reserve Bank	148,594,000
Unused correspondent banking lines of credit from commercial banks for federal funds	$ 20,000,000