Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued capital costs	$ 42,953	$ 47,843
Accrued operating expenses	13,539	10,860
Other accrued liabilities	1,165	115
Total accrued liabilities	$ 57,657	$ 58,818