STOCKHOLDERS' EQUITY - Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended
	Feb. 08, 2016	Apr. 08, 2015	Mar. 31, 2017	Mar. 31, 2016	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			$ 0	$ 120,258
Underwritten Public Offering
Class of Stock [Line Items]
Depository shares issued (in shares)	5,000,000	4,600,000
Price per share of depository shares (in dollars per share)	$ 25	$ 25
Series D 7.375% non-cumulative perpetual
Class of Stock [Line Items]
Non cumulative preferred stock, dividend rate		7.375%
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%
Preferred stock, shares issued (in shares)	125,000
Price per share of depository shares (in dollars per share)	$ 25
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 issued (in shares)	5,000,000
Depository shares to preferred stock ratio	2.50%
Net proceeds from issuance of preferred stock	$ 121,100
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