Lease costs (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Leases [Abstract]
Weighted average remaining lease term	2 years 7 months 17 days
Weighted average discount rate	4.51%
Cash paid for amounts included in the measurement of lease liabilities	$ 11,467
Operating lease cost	11,521
Variable lease cost	399
Short-term lease cost	17,238
Total lease costs	29,158
Lessee, Operating Lease Not Yet Commenced, Value	$ 7,500