FEDERAL HOME LOAN BANK ADVANCES AND OTHER BORROWINGS - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Fixed bank advances	$ 200,000,000	$ 150,000,000
Variable bank advances	$ 880,000,000	$ 340,000,000
FHLB variable-rate, weighted average interest rate	0.78%	0.52%
Line of Credit Facility [Line Items]
Advances from FHLB collateralized	$ 2,890,000,000	$ 3,270,000,000
Other borrowings	67,981,000	67,922,000
Securities sold under repurchase agreements	26,320,000	0
Fair value of securities sold under repurchase agreements	30,200,000
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	$ 68,000,000
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%
Securities
Line of Credit Facility [Line Items]
Advances from FHLB collateralized	$ 696,500,000	321,000,000
Federal Home Loan Bank of San Francisco
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
FHLB stock	37,100,000	$ 41,900,000
Amount of additional available borrowing	$ 1,800,000,000
Minimum
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
FHLB fixed interest rate	0.86%	0.69%
Line of Credit Facility [Line Items]
Securities sold under repurchase agreements, interest rate	1.83%
Maximum
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
FHLB fixed interest rate	3.00%	1.61%
Line of Credit Facility [Line Items]
Securities sold under repurchase agreements, interest rate	1.98%
Weighted Average
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
FHLB fixed interest rate	2.08%	1.02%
Line of Credit Facility [Line Items]
Securities sold under repurchase agreements, interest rate	1.93%
Federal Reserve Bank Advances
Line of Credit Facility [Line Items]
Line of credit facility	$ 191,800,000
Other borrowings	0
Federal Reserve Bank Advances | Securities
Line of Credit Facility [Line Items]
Collateral on line of credit facility	197,600,000
Federal Reserve Bank Advances | Loans
Line of Credit Facility [Line Items]
Collateral on line of credit facility	$ 9,500,000