Leases - Lease Revenue - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Lessor, Lease, Description [Line Items]
Lessor, Sales-type Lease, Renewal Term	50 years		50 years
Lessor, Sales-type Lease, Term of Contract	30 years		30 years
Residual Value of Leased Asset	$ 4,200	$ 3,900	$ 4,200	$ 3,900	$ 4,000
Lease Revenue [Abstract]
Operating leases	18	48	71	143
Sales-type leases	4,588	4,895	13,766	7,039
Total lease revenue	4,606	$ 4,943	13,837	$ 7,182
Operating Leases Payment to be Received [Abstract]
Operating Lease, Payments to be Received, Remainder of Fiscal Year	18		18
Operating Lease, Payments to be Received, Two Years	50		50
Operating Lease, Payments to be Received, Three Years	45		45
Operating Lease, Payments to be Received, Four Years	45		45
Operating Lease, Payments to be Received, Five Years	45		45
Operating Lease, Payments to be Received, Thereafter	94		94
Total lease revenue	297		297
Total Lease Payments to be Received [Abstract]
Lease Payments to be Received, Remainder of Fiscal Year	4,527		4,527
Lease Payments to be Received, Two Years	17,568		17,568
Lease Payments to be Received, Three Years	17,071		17,071
Lease Payments to be Received, Four Years	16,602		16,602
Lease Payments to be Received, Five Years	15,912		15,912
Lease Payments to be Received, Thereafter	267,121		267,121
Total lease revenue	$ 338,801		$ 338,801
Compressed Natural Gas Lease [Member]
Lessor, Lease, Description [Line Items]
Lessor, Sales-type Lease, Term of Contract	10 years		10 years
Residual Value of Leased Asset	$ 0		$ 0
Variable Lease, Payment			0
North Mist Lease [Member]
Lessor, Lease, Description [Line Items]
Residual Value of Leased Asset	0		0
Variable Lease, Payment			0
Sales-type Lease [Member]
Sales-type Leases Payments to be Received [Abstract]
Sales-type Lease, Payments to be Received, Remainder of Fiscal Year	4,509		4,509
Sales-type Lease, Payments to be Received, Two Years	17,518		17,518
Sales-type Lease, Payments to be Received, Three Years	17,026		17,026
Sales-type Lease, Payments to be Received, Four Years	16,557		16,557
Sales-type Lease, Payments to be Received, Five Years	15,867		15,867
Sales-type Lease, Payments to be Received, Thereafter	267,027		267,027
Total lease revenue	338,504		338,504
Less: imputed interest	192,653		192,653
Total leases receivable	$ 145,851		$ 145,851