Commitments and Contingencies - Finance Leases (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Sale Leaseback Transaction [Line Items]
Finance obligations	$ 21,300	$ 21,300	$ 10,400
Total Payments of future minimum lease payments
Total future minimum lease payments	21,300	21,300	10,400
Finance lease costs
Right of use assets obtained in exchange for new finance lease liabilities		200
Restricted Cash
Restricted cash	48,200	48,200
Letter of credit	500	500
Sale Leaseback Agreements
Sale Leaseback Transaction [Line Items]
Finance obligations	72,324	72,324
Total Payments of future minimum lease payments
Remainder of 2018	8,889	8,889
2019	30,030	30,030
2020	6,042	6,042
2021	6,042	6,042
2022	4,296	4,296
2023 and thereafter	17,025	17,025
Total future minimum lease payments	72,324	72,324
Less imputed lease interest	(12,811)	(12,811)
Total lease liabilities	59,513	59,513
Finance lease costs
Amortization of right of use asset	2,193	6,776
Interest on finance obligations	1,837	4,781
Total finance lease cost	4,030	11,557
Right of use assets obtained in exchange for new finance lease liabilities	0
Other information
Cash payments	$ 6,986	$ 26,392
Weighted average remaining lease term	3 years 7 days	3 years 6 months 22 days
Weighted average discount rate	11.20%	11.10%
Finance obligation | Property and equipment
Sale Leaseback Transaction [Line Items]
Finance obligations	$ 2,500	$ 2,500	2,400
Total Payments of future minimum lease payments
Total future minimum lease payments	$ 2,500	$ 2,500	$ 2,400