FAIR VALUE MEASUREMENT AND FAIR VALUE OF FINANCIAL INSTRUMENTS (Details 7) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014	Dec. 31, 2013
Financial Assets:
Cash and cash equivalents	$ 1,886,199		$ 1,039,885		$ 1,884,855	$ 895,820
Short-term investments	325,350		338,714
Securities purchased under resale agreements	1,550,000		1,225,000
Loans held for sale	196,111		45,950
Loans receivable, net	21,116,931	[1]	21,468,270	[1]
Investment in Federal Home Loan Bank stock	28,603		31,239
Investment in Federal Reserve Bank stock	54,556		54,451
Financial Liabilities:
Federal Home Loan Bank advances	317,777		317,241
Securities sold under repurchase agreements	695,000		795,000
Long-term debt	220,905		225,848
Carrying Amount
Financial Assets:
Cash and cash equivalents	1,886,199		1,039,885
Short-term investments	325,350		338,714
Securities purchased under resale agreements	1,550,000		1,225,000
Loans held for sale	196,111		45,950
Loans receivable, net	21,116,931		21,468,270
Investment in Federal Home Loan Bank stock	28,603		31,239
Investment in Federal Reserve Bank stock	54,556		54,451
Accrued interest receivable	86,186		88,303
Financial Liabilities:
Demand, savings and money market deposits	18,786,462		17,896,035
Time deposits	6,376,371		6,112,739
Federal Home Loan Bank advances	317,777		317,241
Securities sold under repurchase agreements	695,000		795,000
Accrued interest payable	12,141		11,303
Long-term debt	220,905		225,848
Fair Value Measurements
Financial Assets:
Cash and cash equivalents	1,886,199		1,039,885
Short-term investments	325,350		338,714
Securities purchased under resale agreements	1,597,101		1,191,060
Loans held for sale	196,111		45,950
Loans receivable, net	20,905,743		20,997,379
Investment in Federal Home Loan Bank stock	28,603		31,239
Investment in Federal Reserve Bank stock	54,556		54,451
Accrued interest receivable	86,186		88,303
Financial Liabilities:
Demand, savings and money market deposits	18,786,462		17,896,035
Time deposits	6,358,260		6,095,217
Federal Home Loan Bank advances	334,286		336,302
Securities sold under repurchase agreements	751,270		870,434
Accrued interest payable	12,141		11,303
Long-term debt	207,906		205,777
Fair Value Measurements | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Assets:
Cash and cash equivalents	1,886,199		1,039,885
Fair Value Measurements | Significant Other Observable Inputs (Level 2)
Financial Assets:
Short-term investments	325,350		338,714
Securities purchased under resale agreements	1,597,101		1,191,060
Loans held for sale	196,111		45,950
Investment in Federal Home Loan Bank stock	28,603		31,239
Investment in Federal Reserve Bank stock	54,556		54,451
Accrued interest receivable	86,186		88,303
Financial Liabilities:
Demand, savings and money market deposits	18,786,462		17,896,035
Federal Home Loan Bank advances	334,286		336,302
Securities sold under repurchase agreements	751,270		870,434
Accrued interest payable	12,141		11,303
Long-term debt	207,906		205,777
Fair Value Measurements | Significant Unobservable Inputs (Level 3)
Financial Assets:
Loans receivable, net	20,905,743		20,997,379
Financial Liabilities:
Time deposits	$ 6,358,260		$ 6,095,217

[1] Loans net of ASC 310-30 discount.