Leases - Components of lease expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
LEASES
Operating lease cost	$ 14,109
Short-term lease cost	7,254
Variable lease cost	521
Sublease income	(72)
Total lease cost	$ 21,812
Operating Leases, Rent Expense, Net		$ 21,600	$ 17,100