Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Accrued Liabilities
Capital expenditures	$ 42,610	$ 35,608
Operating expenses	22,862	14,582
Interest	10,681	10,613
Other	943	838
Accrued liabilities	$ 77,096	$ 61,641