FAIR VALUE MEASUREMENT AND FAIR VALUE OF FINANCIAL INSTRUMENTS (Details 7) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financial assets:
Cash and cash equivalents	$ 1,360,887	$ 1,039,885	$ 895,820	$ 1,323,106
Short-term investments	299,916	338,714
Resale agreements	1,600,000	1,225,000
Loans held for sale	31,958	45,950
Loans receivable, net	23,378,789	21,468,270
Investment in FHLB stock	28,770	31,239
Investment in Federal Reserve Bank stock	54,932	54,451
Customer deposit accounts:
Demand, savings and money market deposits	20,859,086	17,896,035
Time deposits	6,616,895	6,112,739
FHLB advances	1,019,424	317,241
Repurchase agreements	0	795,000
Long-term debt	206,084	225,848
Gross repurchase agreements	450,000	995,000
Carrying amount of repurchase agreements eligible for netting against resale agreements	450,000	200,000
Carrying Amount
Financial assets:
Cash and cash equivalents	1,360,887	1,039,885
Short-term investments	299,916	338,714
Resale agreements	1,600,000	1,225,000
Loans held for sale	31,958	45,950
Loans receivable, net	23,378,789	21,468,270
Investment in FHLB stock	28,770	31,239
Investment in Federal Reserve Bank stock	54,932	54,451
Accrued interest receivable	89,243	88,303
Customer deposit accounts:
Demand, savings and money market deposits	20,859,086	17,896,035
Time deposits	6,616,895	6,112,739
FHLB advances	1,019,424	317,241
Repurchase agreements		795,000
Accrued interest payable	8,848	11,303
Long-term debt	206,084	225,848
Fair Value Measurements
Financial assets:
Cash and cash equivalents	1,360,887	1,039,885
Short-term investments	299,916	338,714
Resale agreements	1,533,961	1,191,060
Loans held for sale	31,958	45,950
Loans receivable, net	23,000,817	20,997,379
Investment in FHLB stock	28,770	31,239
Investment in Federal Reserve Bank stock	54,932	54,451
Accrued interest receivable	89,243	88,303
Customer deposit accounts:
Demand, savings and money market deposits	20,859,086	17,896,035
Time deposits	6,606,942	6,095,217
FHLB advances	1,032,000	336,302
Repurchase agreements		870,434
Accrued interest payable	8,848	11,303
Long-term debt	186,593	205,777
Fair Value Measurements | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	1,360,887	1,039,885
Fair Value Measurements | Significant Other Observable Inputs (Level 2)
Financial assets:
Short-term investments	299,916	338,714
Resale agreements	1,533,961	1,191,060
Loans held for sale	31,958	45,950
Investment in FHLB stock	28,770	31,239
Investment in Federal Reserve Bank stock	54,932	54,451
Accrued interest receivable	89,243	88,303
Customer deposit accounts:
Demand, savings and money market deposits	20,859,086	17,896,035
Time deposits	6,606,942	6,095,217
FHLB advances	1,032,000	336,302
Repurchase agreements		870,434
Accrued interest payable	8,848	11,303
Long-term debt	186,593	205,777
Fair Value Measurements | Significant Unobservable Inputs (Level 3)
Financial assets:
Loans receivable, net	$ 23,000,817	$ 20,997,379