Other Borrowings - Additional Information (Detail) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Debt Disclosure [Abstract]
Security repurchase agreement	$ 0	$ 0
Other collateralized borrowings	12,328,000	$ 9,276,000
Repurchase investment securities sold and pledged as collateral under securities repurchase agreement	12,328,000
FHLB collateral line of credit, maximum borrowings capacity	1,143,065,000
FHLB collateral line of credit, outstanding balance	0
FHLB collateral line of credit, remaining borrowing capacity	1,143,065,000
Loans designated as potential collateral under collateralized line of credit with FHLB	94,351,000
Investment securities designated as potential collateral under collateral line of credit	1,673,789,000
Collateralized line of credit with San Francisco Federal Reserve Bank, maximum borrowings capacity	135,684,000
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	135,684,000
Investment securities designated as potential collateral under collateral line of credit with San Francisco Federal Reserve Bank	218,000
Loans designated as potential collateral under collateral line of credit with San Francisco Federal Reserve Bank	186,187,000
Unused correspondent banking lines of credit from commercial banks for federal funds	$ 15,000,000