Leases - Components of lease expenses (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Components of lease expenses:
Operating lease cost	$ 2,479	$ 7,502
Amortization of assets	1,091	2,496
Interest on lease liabilities	505	1,204
Sublease income	(46)	(139)
Total lease costs	$ 4,029	$ 11,063