Leases - Supplemental balance sheet information (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Right-of-Use Assets under Operating Leases
Operating lease right-of-use assets	$ 17,248
Operating lease right-of-use assets		$ 20,819
Operating lease right-of-use liabilities, current portion	5,459
Operating lease right-of-use liabilities, current portion		5,649
Operating lease right-of-use liabilities, long-term portion	11,789
Operating lease right-of-use liabilities, long-term portion		15,170
Total operating lease liabilities	17,248
Total operating lease liabilities		20,819
Right-of-Use Assets under Finance Leases
Property and equipment, at cost	81,929
Property and equipment, at cost		102,852
Less accumulated depreciation	30,000
Less accumulated depreciation		31,954
Property and equipment under finance lease, net	51,929
Property and equipment under finance lease, net		70,898
Current portion of long-term debt	22,747
Current portion of long-term debt		27,519
Long-term debt	22,896
Long-term debt		33,390
Total finance lease liabilities	$ 45,643
Total finance lease liabilities		$ 60,909