Lease - Components of lease costs (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Components of operating lease costs
Operating lease cost	$ 10,621	$ 10,599	$ 21,251	$ 21,130
Less operating lease and sublease income	(354)	(663)	(972)	(1,050)
Net operating lease cost	10,267	9,936	20,279	20,080
Amortization of ROU assets	147	147	295	295
Interest on lease liabilities	141	150	285	302
Total finance lease cost	$ 288	$ 297	$ 580	$ 597