Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accrued Liabilities
Capital expenditures	$ 42,883	$ 35,608
Operating expenses	24,707	14,582
Interest	1,950	10,613
Other	992	838
Accrued liabilities	$ 70,532	$ 61,641