Leases - Lease Cost (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
Finance lease cost
Amortization of leased assets	$ 1,189	$ 1,049	$ 2,378	$ 2,099
Interest on lease liabilities	2,372	2,511	4,744	5,022
Operating lease cost	883	1,230	1,766	2,460
Total leased cost	$ 4,444	$ 4,790	$ 8,888	$ 9,581
Weighted-average remaining lease term (in years)
Finance leases	9 years 3 months 26 days		9 years 3 months 26 days		9 years 9 months 26 days
Operating leases	5 years 4 months 13 days		5 years 4 months 13 days
Weighted-average discount rate
Finance leases	11.05%		11.05%		11.05%
Operating leases	4.85%		4.85%