EQUITY - Common Stock and Preferred Stock (Details)					12 Months Ended
	Apr. 24, 2015 shares	Mar. 03, 2015 shares	Jan. 01, 2015 shares	May. 28, 2014 shares	Dec. 31, 2015 Vote $ / shares shares	Dec. 31, 2014 $ / shares shares	Dec. 31, 2013 shares
Equity
Common stock, shares authorized					500,000,000	500,000,000
Common stock, par value (in dollars per share) | $ / shares					$ 0.01	$ 0.01
Number of votes a share of outstanding common stock is entitled | Vote					1
Shares reserved for issuance					14,691,018	9,669,896
Preferred stock, shares authorized					100,000,000	100,000,000
Preferred stock, par value (in dollars per share) | $ / shares					$ 0.01	$ 0.01
Stock options
Equity
Exercise price (in dollars per share) | $ / shares					$ 9.75	$ 9.75
Undesignated preferred stock
Equity
Preferred stock, shares authorized					91,600,000
9.25% Series A Preferred Stock
Equity
Preferred stock, shares authorized					2,000,000
Preferred stock, dividend rate (as a percent)					9.25%	9.25%
Preferred stock, liquidation preference (in dollars per share) | $ / shares					$ 25	$ 25
Annual dividend rate per share (in dollars per share) | $ / shares					$ 2.3125
9.25% Series A Preferred Stock | Maximum | Change in control provision
Equity
Ratio for conversion					5.92417
7.875% Series B Preferred Stock
Equity
Preferred stock, shares authorized					3,000,000	3,000,000
Preferred stock, dividend rate (as a percent)					7.875%	7.875%
Preferred stock, liquidation preference (in dollars per share) | $ / shares					$ 25	$ 25
Annual dividend rate per share (in dollars per share) | $ / shares					$ 1.96875
7.875% Series B Preferred Stock | Maximum | Change in control provision
Equity
Ratio for conversion					5.6497
7.125% Series C Preferred Stock
Equity
Preferred stock, shares authorized					3,400,000	3,400,000
Preferred stock, dividend rate (as a percent)					7.125%	7.125%
Preferred stock, liquidation preference (in dollars per share) | $ / shares					$ 25	$ 25
Annual dividend rate per share (in dollars per share) | $ / shares					$ 1.78125
7.125% Series C Preferred Stock | Maximum | Change in control provision
Equity
Ratio for conversion					5.1440
Common Stock
Equity
Shares of common stock issued to redeem common units					268,947	438,631	4,414,950
Stock issued, net on cashless exercise (in shares)					411,239	321,269	327,806
Common Stock | Restricted Stock Awards
Equity
Restricted stock, shares withheld to cover employee tax obligations					36,385	12,588
Common Stock | Stock options
Equity
Stock issued, net on cashless exercise (in shares)					99,738	4,253
Common Stock | Executive officers and employees
Equity
Stock issued (in shares)	16,930	303,915		278,916
Stock forfeited (in shares)						1,756
Common Stock | Outside directors
Equity
Stock issued in lieu of cash for director fees (in shares)					6,246	7,539
Stock issued (in shares)					30,440	32,317
Performance-Based | Restricted Stock Awards
Equity
Vested (in shares)					184,666	45,551	0
Forfeited (in shares)					46,030
Performance-Based | Management | Restricted Stock Awards
Equity
Vested (in shares)			128,185
Forfeited (in shares)			46,030