Commitments and Contingencies - Capital Leases (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Restricted Cash
Restricted cash	$ 39,400
Letter of credit	1,000
Capital Leases
Total Payments of future minimum lease payments
2018	25,528
2019	19,930
2020	6,042
2021	6,043
2022	4,296
2023 and Thereafter	11,510
Total future minimum lease payments	73,349
Imputed Interest of future minimum lease payments
2018	3,322
2019	2,403
2020	1,800
2021	1,316
2022	705
2023 and Thereafter	1,021
Total future minimum lease payments: Imputed Interest	10,567
Net Present Value of future minimum lease payments
2018	22,206
2019	17,527
2020	4,242
2021	4,727
2022	3,591
2023 and Thereafter	10,489
Total future minimum lease payments: Net Present Value	62,782
Cash received for future services	9,200	$ 10,400
Long-term debt. | Capital Leases
Sale Leaseback Transaction [Line Items]
Sale-leaseback liability	64,600
Finance obligation
Sale Leaseback Transaction [Line Items]
Sale-leaseback liability	$ 2,200	$ 2,300