FAIR VALUE MEASUREMENT AND FAIR VALUE OF FINANCIAL INSTRUMENTS (Details 6) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Financial assets:
Cash and cash equivalents	$ 1,592,796	$ 1,360,887	$ 1,877,914	$ 1,039,885
Short-term investments	229,979	299,916
Resale agreements	1,850,000	1,600,000
Held-to-maturity investment security	159,208	0
Loans held for sale	51,290	31,958
Loans receivable, net	23,969,599	23,378,789
Investment in FHLB stock	18,158	28,770
Investment in Federal Reserve Bank stock	55,216	54,932
Customer deposit accounts:
Short-term borrowings	29,499	0
FHLB advances	320,526	1,019,424
Repurchase agreements	200,000	0
Long-term debt	196,204	206,084
Carrying amount of repurchase agreements eligible for netting against resale agreements	250,000	450,000
Gross repurchase agreements	450,000	450,000
Carrying Amount
Financial assets:
Cash and cash equivalents	1,592,796	1,360,887
Short-term investments	229,979	299,916
Resale agreements	1,850,000	1,600,000
Held-to-maturity investment security	159,208
Loans held for sale	51,290	31,958
Loans receivable, net	23,969,599	23,378,789
Investment in FHLB stock	18,158	28,770
Investment in Federal Reserve Bank stock	55,216	54,932
Accrued interest receivable	86,503	89,243
Customer deposit accounts:
Demand, savings and money market deposits	22,484,884	20,859,086
Time deposits	5,732,359	6,616,895
Short-term borrowings	29,499
FHLB advances	320,526	1,019,424
Repurchase agreements	200,000
Accrued interest payable	8,053	8,848
Long-term debt	196,204	206,084
Fair Value Measurements
Financial assets:
Cash and cash equivalents	1,592,796	1,360,887
Short-term investments	229,979	299,916
Resale agreements	1,850,427	1,533,961
Held-to-maturity investment security	158,279
Loans held for sale	51,290	31,958
Loans receivable, net	23,928,765	23,000,817
Investment in FHLB stock	18,158	28,770
Investment in Federal Reserve Bank stock	55,216	54,932
Accrued interest receivable	86,503	89,243
Customer deposit accounts:
Demand, savings and money market deposits	22,484,884	20,859,086
Time deposits	5,736,110	6,606,942
Short-term borrowings	29,499
FHLB advances	332,595	1,032,000
Repurchase agreements	268,353
Accrued interest payable	8,053	8,848
Long-term debt	196,826	186,593
Fair Value Measurements | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	1,592,796	1,360,887
Fair Value Measurements | Significant Other Observable Inputs (Level 2)
Financial assets:
Short-term investments	229,979	299,916
Resale agreements	1,850,427	1,533,961
Loans held for sale	51,290	31,958
Investment in FHLB stock	18,158	28,770
Investment in Federal Reserve Bank stock	55,216	54,932
Accrued interest receivable	86,503	89,243
Customer deposit accounts:
Demand, savings and money market deposits	22,484,884	20,859,086
Time deposits	5,736,110	6,606,942
Short-term borrowings	29,499
FHLB advances	332,595	1,032,000
Repurchase agreements	268,353
Accrued interest payable	8,053	8,848
Long-term debt	196,826	186,593
Fair Value Measurements | Significant Unobservable Inputs (Level 3)
Financial assets:
Held-to-maturity investment security	158,279
Loans receivable, net	$ 23,928,765	$ 23,000,817