Leases - Lease Revenue (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 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	$ 4,100,000	$ 3,800,000	$ 4,100,000	$ 3,800,000	$ 4,000,000.0
Lease Revenue [Abstract]
Operating leases	25,000	47,000	53,000	95,000
Sales-type leases	4,588,000	2,085,000	9,178,000	2,145,000
Total lease revenue	4,613,000	$ 2,132,000	9,231,000	$ 2,240,000
Operating Leases Payment to be Received [Abstract]
Operating Lease, Payments to be Received, Remainder of Fiscal Year	35,000		35,000
Operating Lease, Payments to be Received, Two Years	50,000		50,000
Operating Lease, Payments to be Received, Three Years	45,000		45,000
Operating Lease, Payments to be Received, Four Years	45,000		45,000
Operating Lease, Payments to be Received, Five Years	45,000		45,000
Operating Lease, Payments to be Received, Thereafter	94,000		94,000
Total lease revenue	314,000		314,000
Total Lease Payments to be Received [Abstract]
Lease Payments to be Received, Remainder of Fiscal Year	9,078,000		9,078,000
Lease Payments to be Received, Two Years	17,568,000		17,568,000
Lease Payments to be Received, Three Years	17,071,000		17,071,000
Lease Payments to be Received, Four Years	16,602,000		16,602,000
Lease Payments to be Received, Five Years	15,912,000		15,912,000
Lease Payments to be Received, Thereafter	267,121,000		267,121,000
Total lease revenue	$ 343,352,000		$ 343,352,000
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	9,043,000		9,043,000
Sales-type Lease, Payments to be Received, Two Years	17,518,000		17,518,000
Sales-type Lease, Payments to be Received, Three Years	17,026,000		17,026,000
Sales-type Lease, Payments to be Received, Four Years	16,557,000		16,557,000
Sales-type Lease, Payments to be Received, Five Years	15,867,000		15,867,000
Sales-type Lease, Payments to be Received, Thereafter	267,027,000		267,027,000
Total lease revenue	343,038,000		343,038,000
Less: imputed interest	195,806,000		195,806,000
Total leases receivable	$ 147,232,000		$ 147,232,000