Other Assets and Accrued Liabilities - Long-Term Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Other Liabilities Disclosure [Abstract]
Non-current portion of deferred revenues	$ 12,659		$ 14,030
Other	1,908		1,263
Other liabilities	$ 14,567	$ 14,093	$ 15,293