FAIR VALUE MEASUREMENT AND FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Available-for-sale investment securities
Total available-for-sale investment securities	$ 2,841,085		$ 2,626,365
U.S. Treasury securities
Available-for-sale investment securities
Total available-for-sale investment securities	1,172,226		873,435
U.S. government agency and U.S. government sponsored enterprise debt securities
Available-for-sale investment securities
Total available-for-sale investment securities	411,966		311,024
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities
Available-for-sale investment securities
Total available-for-sale investment securities	95,235		141,420
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities
Available-for-sale investment securities
Total available-for-sale investment securities	727,356		791,088
Municipal securities
Available-for-sale investment securities
Total available-for-sale investment securities	191,246		250,448
Other residential mortgage-backed securities | Investment grade
Available-for-sale investment securities
Total available-for-sale investment securities	51,501	[1]	53,918	[1]
Other commercial mortgage-backed securities | Investment grade
Available-for-sale investment securities
Total available-for-sale investment securities			34,053	[1]
Corporate debt securities | Investment grade
Available-for-sale investment securities
Total available-for-sale investment securities	140,401	[1]	115,182	[1]
Corporate debt securities | Non-investment grade
Available-for-sale investment securities
Total available-for-sale investment securities	9,501	[1]	14,681	[1]
Other securities
Available-for-sale investment securities
Total available-for-sale investment securities	41,653		41,116
Fair Value, Measurements, Recurring
Available-for-sale investment securities
Total available-for-sale investment securities	2,841,085		2,626,365
Fair Value, Measurements, Recurring | Foreign exchange options
Derivative
Derivative assets	3,683		6,136
Fair Value, Measurements, Recurring | Interest rate swaps on certificates of deposits
Derivative
Derivative liabilities	(6,370)		(9,922)
Fair Value, Measurements, Recurring | Interest rate swaps and caps
Derivative
Derivative assets	66,060		41,534
Derivative liabilities	(66,914)		(41,779)
Fair Value, Measurements, Recurring | Foreign exchange contracts
Derivative
Derivative assets	13,340		8,123
Derivative liabilities	(13,080)		(9,171)
Fair Value, Measurements, Recurring | Embedded derivative liabilities
Derivative
Derivative liabilities	(3,412)		(3,392)
Fair Value, Measurements, Recurring | U.S. Treasury securities
Available-for-sale investment securities
Total available-for-sale investment securities	1,172,226		873,435
Fair Value, Measurements, Recurring | U.S. government agency and U.S. government sponsored enterprise debt securities
Available-for-sale investment securities
Total available-for-sale investment securities	411,966		311,024
Fair Value, Measurements, Recurring | U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities
Available-for-sale investment securities
Total available-for-sale investment securities	95,235		141,420
Fair Value, Measurements, Recurring | U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities
Available-for-sale investment securities
Total available-for-sale investment securities	727,356		791,088
Fair Value, Measurements, Recurring | Municipal securities
Available-for-sale investment securities
Total available-for-sale investment securities	191,246		250,448
Fair Value, Measurements, Recurring | Other residential mortgage-backed securities | Investment grade
Available-for-sale investment securities
Total available-for-sale investment securities	51,501		53,918
Fair Value, Measurements, Recurring | Other commercial mortgage-backed securities | Investment grade
Available-for-sale investment securities
Total available-for-sale investment securities			34,053
Fair Value, Measurements, Recurring | Corporate debt securities | Investment grade
Available-for-sale investment securities
Total available-for-sale investment securities	140,401		115,182
Fair Value, Measurements, Recurring | Corporate debt securities | Non-investment grade
Available-for-sale investment securities
Total available-for-sale investment securities	9,501		14,681
Fair Value, Measurements, Recurring | Other securities
Available-for-sale investment securities
Total available-for-sale investment securities	41,653		41,116
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Available-for-sale investment securities
Total available-for-sale investment securities	1,204,703		905,540
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury securities
Available-for-sale investment securities
Total available-for-sale investment securities	1,172,226		873,435
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other securities
Available-for-sale investment securities
Total available-for-sale investment securities	32,477		32,105
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Available-for-sale investment securities
Total available-for-sale investment securities	1,636,382		1,714,297
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Foreign exchange options
Derivative
Derivative assets	3,683		6,136
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Interest rate swaps on certificates of deposits
Derivative
Derivative liabilities	(6,370)		(9,922)
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Interest rate swaps and caps
Derivative
Derivative assets	66,060		41,534
Derivative liabilities	(66,914)		(41,779)
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Foreign exchange contracts
Derivative
Derivative assets	13,340		8,123
Derivative liabilities	(13,080)		(9,171)
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. government agency and U.S. government sponsored enterprise debt securities
Available-for-sale investment securities
Total available-for-sale investment securities	411,966		311,024
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities
Available-for-sale investment securities
Total available-for-sale investment securities	95,235		141,420
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities
Available-for-sale investment securities
Total available-for-sale investment securities	727,356		791,088
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Municipal securities
Available-for-sale investment securities
Total available-for-sale investment securities	191,246		250,448
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other residential mortgage-backed securities | Investment grade
Available-for-sale investment securities
Total available-for-sale investment securities	51,501		53,918
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other commercial mortgage-backed securities | Investment grade
Available-for-sale investment securities
Total available-for-sale investment securities			34,053
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Corporate debt securities | Investment grade
Available-for-sale investment securities
Total available-for-sale investment securities	140,401		115,182
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Corporate debt securities | Non-investment grade
Available-for-sale investment securities
Total available-for-sale investment securities	9,501		8,153
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other securities
Available-for-sale investment securities
Total available-for-sale investment securities	9,176		9,011
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Available-for-sale investment securities
Total available-for-sale investment securities			6,528
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Embedded derivative liabilities
Derivative
Derivative liabilities	(3,412)		(3,392)
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Corporate debt securities | Non-investment grade
Available-for-sale investment securities
Total available-for-sale investment securities			$ 6,528

[1] Available-for-sale investment securities rated BBB- or higher by S&P or Baa3 or higher by Moody's are considered investment grade. Conversely, available-for-sale investment securities rated lower than BBB- by S&P or lower than Baa3 by Moody's are considered non-investment grade.