STOCKHOLDERS' EQUITY - Share Repurchases (Details) - USD ($)					12 Months Ended
	Dec. 18, 2017	Jun. 12, 2017	Sep. 14, 2016	May 16, 2016	Dec. 31, 2017	Dec. 31, 2016	Apr. 22, 2016
Class of Stock [Line Items]
Aggregate purchase price, repurchase of common stock					$ 886,010,000	$ 290,134,000
Cash Tender Offer
Class of Stock [Line Items]
Shares repurchase fees and expenses				$ 301,000
Cash Tender Offer | Common Stock
Class of Stock [Line Items]
Repurchase of common stock (in shares)				10,000,000
Aggregate purchase price, repurchase of common stock				$ 210,000,000
Share price of stock repurchased (in usd per share)				$ 21
Urban Partners II, LLC | December 2017 Share Repurchase | Common Stock
Class of Stock [Line Items]
Repurchase of common stock (in shares)	14,090,909
Aggregate purchase price, repurchase of common stock	$ 310,000,000
Share price of stock repurchased (in usd per share)	$ 22
Urban Partners II, LLC | June 2017 Share Repurchase | Common Stock
Class of Stock [Line Items]
Repurchase of common stock (in shares)		26,181,818
Aggregate purchase price, repurchase of common stock		$ 576,000,000
Share price of stock repurchased (in usd per share)		$ 22
Urban Partners II, LLC | September 2016 Share Repurchase | Common Stock
Class of Stock [Line Items]
Repurchase of common stock (in shares)			3,628,116
Aggregate purchase price, repurchase of common stock			$ 79,819,000
Share price of stock repurchased (in usd per share)			$ 22
Urban Partners II, LLC | Cash Tender Offer | Common Stock
Class of Stock [Line Items]
Aggregate purchase price, repurchase of common stock				$ 208,140,000
Registration statement | Series A Preferred Stock
Class of Stock [Line Items]
Warrant right to purchase a share of Common Stock							0.25