Lessor Leases - Operating Lease Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Operating Leased Assets [Line Items]
Rental income	$ 3,365	$ 3,011	$ 6,652	$ 5,801
Total property and equipment, net	52,847		52,847		$ 51,500
Accumulated depreciation and amortization	107,175		107,175		100,789
Depreciation	$ 4,400	3,800	$ 8,400	7,300
Minimum
Operating Leased Assets [Line Items]
Term of Contract ( in years )	1 year		1 year
Maximum
Operating Leased Assets [Line Items]
Term of Contract ( in years )	7 years		7 years
Equipment
Operating Leased Assets [Line Items]
Total property and equipment, net	$ 2,400		$ 2,400		2,600
Accumulated depreciation and amortization	1,300		1,300		$ 1,200
Depreciation	$ 300	$ 100	$ 400	$ 200