Income Taxes - Effective Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Apr. 12, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SUCCESSOR
Effective Income Tax Rate [Line Items]
Income (loss) before tax		$ (46,935)	$ 123,819	$ 145,159
Statutory rate		35.00%	21.00%	35.00%
Tax expense (benefit) at federal statutory rate		$ (16,427)	$ 26,002	$ 50,806
Increase (decrease)
Plant differences, including AFUDC flowthrough		(881)	(401)	743
Amortization of investment tax credits		(371)	(236)	(662)
State income taxes, net of federal benefit		1,844	6,288	5,047
Nondeductible merger costs		(844)	0	2
Return to accrual adjustment		(2,943)	(193)	(608)
TCJA		0	(19)	(46,291)
NMTC		(181)	(1,578)	313
Other		(3,019)	(481)	(2,271)
Total tax expense (benefit)		$ (22,822)	$ 29,382	$ 7,079
Effective rate		48.60%	23.70%	4.90%
PREDECESSOR
Effective Income Tax Rate [Line Items]
Income (loss) before tax	$ (492)
Statutory rate	35.00%
Tax expense (benefit) at federal statutory rate	$ (172)
Increase (decrease)
Plant differences, including AFUDC flowthrough	823
Amortization of investment tax credits	(124)
State income taxes, net of federal benefit	(3,078)
Nondeductible merger costs	4,282
Return to accrual adjustment	0
TCJA	0
NMTC	(158)
Other	1,895
Total tax expense (benefit)	$ 3,468
Effective rate	(704.90%)
CLECO POWER
Effective Income Tax Rate [Line Items]
Income (loss) before tax			$ 218,181	$ 218,069	$ 57,497
Statutory rate			21.00%	35.00%	35.00%
Tax expense (benefit) at federal statutory rate			$ 45,818	$ 76,324	$ 20,124
Increase (decrease)
Plant differences, including AFUDC flowthrough			(401)	743	(58)
Amortization of investment tax credits			(236)	(662)	(494)
State income taxes, net of federal benefit			11,080	7,583	1,999
Return to accrual adjustment			483	(284)	(2,646)
TCJA			(19)	(14,292)	0
Other			(801)	(2,081)	(556)
Total tax expense (benefit)			$ 55,924	$ 67,331	$ 18,369
Effective rate			25.60%	30.90%	31.90%