Leases - Components of lease expense (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Lease cost
Short-term operating lease expense	$ 1,974
Long-term operating lease expense	2,185
Total operating lease expense	4,159
Amortization of right-of-use assets	5,440
Interest on lease liabilities	1,382
Total finance lease expense	$ 6,822
Weighted average remaining lease term (in years): Operating leases	3 years
Weighted average remaining lease term (in years): Finance leases	2 years 7 months 6 days
Weighted average discount rate: Operating leases (as a percent)	14.40%
Weighted average discount rate: Operating leases (as a percent)	8.00%
Operating cash outflows from operating leases	$ 4,159
Operating cash outflows from finance leases	1,382
Financing cash outflows from finance leases	11,423
Right-of-use asset obtained in exchange for operating lease liability	0
Right-of-use asset obtained in exchange for fiance lease liability	$ 6,144