Units Outstanding (Details) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Units Outstanding
Outstanding as of January 1,	100,756,999	96,028,494
Options exercised	541,073	1,110,070
Units issued	4,600,583	4,193,445
Units retired	(5,854,170)	(575,010)
Outstanding as of December 31,	100,044,485	100,756,999