STOCKHOLDERS' EQUITY - Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands			9 Months Ended
	Feb. 08, 2016	Apr. 08, 2015	Sep. 30, 2016	Sep. 30, 2015	Apr. 01, 2016
Class of Stock [Line Items]
Preferred stock, authorized (in shares)			50,000,000
Preferred stock, par value (in dollars per share)			$ 0.01
Preferred stock, liquidation preference per share (in dollars per share)			$ 1,000
Net proceeds from issuance of preferred stock			$ 120,255	$ 110,873
Underwritten Public Offering
Class of Stock [Line Items]
Price per share of depository shares (in dollars per share)	$ 25	$ 25
Depository shares issued (in shares)	5,000,000	4,600,000
Series D 7.375% non-cumulative perpetual
Class of Stock [Line Items]
Preferred stock, liquidation preference per share (in dollars per share)		$ 1,000
Issuance of depositary shares		4,000,000
Depository shares to preferred stock ratio		2.50%
Non cumulative preferred stock, dividend rate		7.375%
Price per share of depository shares (in dollars per share)		$ 25
Net proceeds from issuance of preferred stock		$ 96,900
Additional depositary shares to cover over-allotments		600,000
Preferred stock, shares issued (in shares)		115,000
Series D 7.375% non-cumulative perpetual | Over Allotment Option
Class of Stock [Line Items]
Net proceeds from issuance of preferred stock		$ 14,500
Underwriters option period		30 days
Series D 7.375% non-cumulative perpetual | Underwritten Public Offering
Class of Stock [Line Items]
Preferred stock, liquidation preference per share (in dollars per share)		$ 1,000
Depository shares to preferred stock ratio		2.50%
Series E 7.00% non-cumulative perpetual
Class of Stock [Line Items]
Preferred stock, liquidation preference per share (in dollars per share)	$ 1,000
Depository shares to preferred stock ratio	2.50%
Non cumulative preferred stock, dividend rate	7.00%
Price per share of depository shares (in dollars per share)	$ 25
Preferred stock, shares issued (in shares)	125,000
Series E 7.00% non-cumulative perpetual | Underwritten Public Offering
Class of Stock [Line Items]
Preferred stock, liquidation preference per share (in dollars per share)	$ 1,000
Depository shares to preferred stock ratio	2.50%
Net proceeds from issuance of preferred stock	$ 121,100
Depository shares issued (in shares)	5,000,000
Series A Non-cumulative perpetual
Class of Stock [Line Items]
Preferred stock, liquidation preference per share (in dollars per share)					$ 1,000
Preferred stock, shares redeemed (in shares)					32,000
Series B Non-cumulative perpetual
Class of Stock [Line Items]
Preferred stock, shares redeemed (in shares)					10,000