Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Allowance for doubtful accounts	$ 0.3	$ 0.3
Limited partners' units, issued	72,282,942	71,659,385
Limited partners' units, outstanding	72,282,942	71,659,385
Preferred units, issued	71,257,445	71,257,445
Preferred units, outstanding (in units)	71,257,445	71,257,445
CMLP
Allowance for doubtful accounts	$ 0.3	$ 0.3