Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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Name:	us-gaap_StockRepurchasedDuringPeriodShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

EQUITY - Repurchase Program (Details) - 2015 Unit Repurchase Program - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	May 03, 2018
Class of Stock [Line Items]
Unit repurchase program, authorized amount					$ 500,000,000
Class A Common Stock
Class of Stock [Line Items]
Units repurchased (in units)	1,100,000	0	3,300,000	0