Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Allowance for doubtful accounts	$ 1.9	$ 0.4
Limited partners' units, issued	69,499,741	68,555,305
Limited partners' units, outstanding	69,499,741	68,555,305
Preferred units, issued	66,533,415	60,718,245
Preferred units, outstanding	66,533,415	60,718,245
CMLP
Allowance for doubtful accounts	$ 0.0	$ 0.0