Leases - Cottonwood Sale Leaseback Agreement (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)
Lessor, Lease, Description [Line Items]
Depreciation expense	$ 6.6	$ 16.1
Cottonwood Energy
Lessor, Lease, Description [Line Items]
Fixed lease payments per year	$ 40.0	$ 40.0