Leased Property (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Less: accumulated depreciation	$ (16,394)		$ (16,394)		$ (11,812)
Leased property, net	95,621		95,621		87,065
Leased property.
Leased property under capital lease	112,015		112,015		98,877
Less: accumulated depreciation	(16,394)		(16,394)		(11,812)
Leased property, net	95,621		95,621		$ 87,065
Depreciation	$ 2,400	$ 1,700	$ 4,600	$ 3,300