STOCKHOLDERS' EQUITY - Summary of Preferred Stock (Details) - USD ($) $ in Thousands			9 Months Ended	12 Months Ended
	Feb. 08, 2016	Apr. 08, 2015	Sep. 30, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Preferred stock, authorized (in shares)			50,000,000
Carrying Value			$ 269,071	$ 190,750
Series D 7.375% non-cumulative perpetual
Class of Stock [Line Items]
Non cumulative preferred stock, dividend rate		7.375%
Series E 7.00% non-cumulative perpetual
Class of Stock [Line Items]
Non cumulative preferred stock, dividend rate	7.00%
Preferred Stock
Class of Stock [Line Items]
Preferred stock, authorized (in shares)			280,250.00	197,250.00
Preferred stock, shares outstanding (in shares)			280,250	197,250
Liquidation Preference			$ 280,250	$ 197,250
Carrying Value			$ 269,071	$ 190,750
Preferred Stock | Series A Non-cumulative perpetual
Class of Stock [Line Items]
Preferred stock, authorized (in shares)			0	32,000
Preferred stock, shares outstanding (in shares)			0	32,000
Liquidation Preference			$ 0	$ 32,000
Carrying Value			$ 0	$ 31,934
Preferred Stock | Series B Non-cumulative perpetual
Class of Stock [Line Items]
Preferred stock, authorized (in shares)			0	10,000
Preferred stock, shares outstanding (in shares)			0	10,000
Liquidation Preference			$ 0	$ 10,000
Carrying Value			$ 0	$ 10,000
Preferred Stock | Series C 8.00% non-cumulative perpetual
Class of Stock [Line Items]
Preferred stock, authorized (in shares)			40,250	40,250
Preferred stock, shares outstanding (in shares)			40,250	40,250
Non cumulative preferred stock, dividend rate			8.00%	8.00%
Liquidation Preference			$ 40,250	$ 40,250
Carrying Value			$ 37,943	$ 37,943
Preferred Stock | Series D 7.375% non-cumulative perpetual
Class of Stock [Line Items]
Preferred stock, authorized (in shares)			115,000	115,000
Preferred stock, shares outstanding (in shares)			115,000	115,000
Non cumulative preferred stock, dividend rate			7.375%	7.375%
Liquidation Preference			$ 115,000	$ 115,000
Carrying Value			$ 110,873	$ 110,873
Preferred Stock | Series E 7.00% non-cumulative perpetual
Class of Stock [Line Items]
Preferred stock, authorized (in shares)			125,000	0
Preferred stock, shares outstanding (in shares)			125,000	0
Non cumulative preferred stock, dividend rate			7.00%	7.00%
Liquidation Preference			$ 125,000	$ 0
Carrying Value			$ 120,255	$ 0