Other Assets and Accrued Liabilities - Long-Term Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Deferred contract costs	$ 15,953		$ 0
Other	4,143		2,914
Deferred charges and other assets, net	34,021	$ 29,797	13,690
Interest rate swap
Derivatives, Fair Value [Line Items]
Interest rate swaps	$ 13,925		$ 10,776