Intangible Assets and Goodwill - Intangible Assets (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2008	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	$ 69,016,000		$ 45,948,000
Trade name
Finite-Lived Intangible Assets [Line Items]
Residual value	$ 0
Finite-lived intangible asset, useful life	20 years
Power supply agreements
Finite-Lived Intangible Assets [Line Items]
Residual value	$ 0
Power supply agreements | Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	5 years
Power supply agreements | Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	17 years
CLECO POWER
Finite-Lived Intangible Assets [Line Items]
Residual value	$ 0
Accumulated amortization	$ 151,453,000	$ 0	$ 135,836,000
CLECO POWER | Cleco Katrina/Rita right to bill and collect storm recovery charges
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired		177,500,000
CLECO POWER | Cleco Katrina/Rita right to bill and collect storm recovery charges from customers, net of financing costs
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired		176,000,000
CLECO POWER | Financing costs
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired		$ 1,500,000