Supplemental Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Accrued Liabilities [Abstract]
Accrued and other liabilities	$ 20,433		$ 16,250
Accrued interest	5,852		5,448
Accrued maintenance	3,850		2,688
Accrued Income Taxes	2,931		1,564
Accrued Capital Expenditures, Current	2,827		$ 2,818
Increase (reduction) in capital expenditure accrual	$ 52	$ 117