Commitments and Contingencies - Finance Leases (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
Total Payments of future minimum lease payments
Remainder of 2019	$ 19,379		$ 19,379
2020	38,056		38,056
2021	33,059		33,059
2022	25,197		25,197
2023	22,631		22,631
2024 and thereafter	44,534		44,534
Total future minimum lease payments	182,856		182,856
Less imputed lease interest	(54,466)		(54,466)
Sale of future services	59,804		59,804
Total lease liabilities	188,194		188,194
Finance lease costs
Right of use assets obtained in exchange for new finance lease liabilities	60	$ 0	60	$ 300
Restricted Cash
Restricted cash	32,500		32,500
Letter of credit	82,900		82,900
Sale Leaseback Agreements
Total Payments of future minimum lease payments
Total lease liabilities	$ 28,800		28,800		$ 81,900
Finance lease costs
Amortization of right of use asset			1,558	3,017
Interest on finance obligations			2,656	2,944
Total finance lease cost			4,214	5,961
Other information
Cash payments			$ 55,913	$ 19,406
Weighted average remaining lease term (years)	3 years 3 months	3 years 8 months 12 days	3 years 3 months	3 years 8 months 12 days
Weighted average discount rate	10.80%	10.70%	10.80%	10.70%
Finance Lease [Member]
Total Payments of future minimum lease payments
Remainder of 2019	$ 3,361		$ 3,361
2020	6,722		6,722
2021	6,722		6,722
2022	4,975		4,975
2023	3,176		3,176
2024 and thereafter	16,154		16,154
Total future minimum lease payments	41,110		41,110
Less imputed lease interest	(12,339)		(12,339)
Sale of future services	59,804		59,804
Total lease liabilities	88,575		88,575
Other Leased Property [Member]
Total Payments of future minimum lease payments
Remainder of 2019	225		225
2020	425		425
2021	407		407
2022	390		390
2023	366		366
2024 and thereafter	1,565		1,565
Total future minimum lease payments	3,378		3,378
Less imputed lease interest	(989)		(989)
Total lease liabilities	2,389		2,389
Finance obligation
Restricted Cash
Letter of credit	500		500
Finance obligation | Property and equipment
Total Payments of future minimum lease payments
Total future minimum lease payments	$ 2,400		$ 2,400