FEDERAL HOME LOAN BANK ADVANCES AND OTHER BORROWINGS - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Fixed bank advances	$ 700,000,000	$ 200,000,000
Variable bank advances	$ 70,000,000	$ 730,000,000
FHLB variable-rate, weighted average interest rate	0.38%	0.27%
Advances from FHLB collateralized	$ 3,790,000,000	$ 3,380,000,000
Line of Credit Facility [Line Items]
Other borrowings	49,903,000	0
Securities sold under repurchase agreements	0	0
Line of Credit | Unsecured Federal Funds Line of Credit
Line of Credit Facility [Line Items]
Line of credit facility	210,000,000
Line of Credit | Line Of Credit Facility Maturing April 18, 2017
Line of Credit Facility [Line Items]
Line of credit facility	75,000,000
Line of Credit | Line of Credit Facility Maturing March 28, 2016
Line of Credit Facility [Line Items]
Other borrowings	$ 50,000,000
Line of Credit | Line of Credit Facility Maturing March 28, 2016 | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.25%
Federal Home Loan Bank of San Francisco
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
FHLB stock	$ 43,300,000	$ 39,200,000
Amount of additional available borrowing	$ 2,240,000,000
Minimum
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
FHLB fixed interest rate	0.40%	0.50%
Maximum
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
FHLB fixed interest rate	1.61%	1.61%
Weighted Average
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
FHLB fixed interest rate	0.54%	0.89%
Federal Reserve Bank Advances
Line of Credit Facility [Line Items]
Line of credit facility	$ 148,200,000
Other borrowings	0
Federal Reserve Bank Advances | Loans
Line of Credit Facility [Line Items]
Collateral on line of credit facility	7,800,000
Federal Reserve Bank Advances | Securities
Line of Credit Facility [Line Items]
Collateral on line of credit facility	$ 158,700,000