Units Outstanding (Details) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Units Outstanding
Outstanding as of December 31, 2017 (in units)	268,659,333
Options exercised (in units)	235,105	300,000
Units issued (in units)	949,185
Units retired (in units)	(3,686)
Balance as of March 31, 2018 (in units)	269,839,937
Limited Partners' Capital Account [Line Items]
Units purchased and retired (in units)	3,686
AB Units
Units Outstanding
Units retired (in units)	(1,150)
Limited Partners' Capital Account [Line Items]
Units purchased and retired (in units)	1,150