Summary of Significant Accounting Policies - Total Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Accrued capital expenditures	$ 28,711	$ 17,775
Accrued incentive compensation	16,503	20,898
Accrued property taxes	4,090	3,175
Accrued other	3,327	9,104
TOTAL ACCRUED LIABILITIES	$ 52,631	$ 50,952