Units Outstanding (Details)	9 Months Ended
	Sep. 30, 2017 shares
Units Outstanding
Outstanding as of December 31, 2016 (in units)	96,652,190
Options exercised (in units)	1,039,632
Units issued (in units)	1,944,310
Units retired (in units)	(6,009,819)
Outstanding as of September 30, 2017 (in units)	93,626,313