FAIR VALUE MEASUREMENT AND FAIR VALUE OF FINANCIAL INSTRUMENTS (Details 8) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Financial Assets:
Cash and cash equivalents		$ 1,877,914	$ 1,039,885	$ 1,246,044	$ 895,820
Short-term investments		274,838	338,714
Securities purchased under resale agreements ("resale agreements")		1,100,000	1,225,000
Loans held for sale		195,427	45,950
Loans receivable, net	[1]	21,697,435	21,468,270
Investment in Federal Home Loan Bank ("FHLB") stock		18,155	31,239
Investment in Federal Reserve Bank stock		54,675	54,451
Financial Liabilities:
Short-term borrowings		3,271
FHLB advances		318,322	317,241
Securities sold under repurchase agreements ("repurchase agreements")		400,000	795,000
Long-term debt		215,964	225,848
Carrying Amount
Financial Assets:
Cash and cash equivalents		1,877,914	1,039,885
Short-term investments		274,838	338,714
Securities purchased under resale agreements ("resale agreements")		1,100,000	1,225,000
Loans held for sale		195,427	45,950
Loans receivable, net		21,697,435	21,468,270
Investment in Federal Home Loan Bank ("FHLB") stock		18,155	31,239
Investment in Federal Reserve Bank stock		54,675	54,451
Accrued interest receivable		81,575	88,303
Financial Liabilities:
Demand, savings and money market deposits		18,872,270	17,896,035
Time deposits		6,655,950	6,112,739
Short-term borrowings		3,271
FHLB advances		318,322	317,241
Securities sold under repurchase agreements ("repurchase agreements")		400,000	795,000
Accrued interest payable		10,762	11,303
Long-term debt		215,964	225,848
Fair Value Measurements
Financial Assets:
Cash and cash equivalents		1,877,914	1,039,885
Short-term investments		274,838	338,714
Securities purchased under resale agreements ("resale agreements")		1,091,775	1,191,060
Loans held for sale		197,813	45,950
Loans receivable, net		21,460,209	20,997,379
Investment in Federal Home Loan Bank ("FHLB") stock		18,155	31,239
Investment in Federal Reserve Bank stock		54,675	54,451
Accrued interest receivable		81,575	88,303
Financial Liabilities:
Demand, savings and money market deposits		18,872,270	17,896,035
Time deposits		6,640,165	6,095,217
Short-term borrowings		3,271
FHLB advances		334,284	336,302
Securities sold under repurchase agreements ("repurchase agreements")		388,498	870,434
Accrued interest payable		10,762	11,303
Long-term debt		193,157	205,777
Fair Value Measurements | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Assets:
Cash and cash equivalents		1,877,914	1,039,885
Fair Value Measurements | Significant Other Observable Inputs (Level 2)
Financial Assets:
Short-term investments		274,838	338,714
Securities purchased under resale agreements ("resale agreements")		1,091,775	1,191,060
Loans held for sale		197,813	45,950
Investment in Federal Home Loan Bank ("FHLB") stock		18,155	31,239
Investment in Federal Reserve Bank stock		54,675	54,451
Accrued interest receivable		81,575	88,303
Financial Liabilities:
Demand, savings and money market deposits		18,872,270	17,896,035
Time deposits		6,640,165	6,095,217
Short-term borrowings		3,271
FHLB advances		334,284	336,302
Securities sold under repurchase agreements ("repurchase agreements")		388,498	870,434
Accrued interest payable		10,762	11,303
Long-term debt		193,157	205,777
Fair Value Measurements | Significant Unobservable Inputs (Level 3)
Financial Assets:
Loans receivable, net		$ 21,460,209	$ 20,997,379

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