Other Assets and Accrued Liabilities - Long-Term Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Other Liabilities Disclosure [Abstract]
Non-current portion of deferred revenues	$ 12,613		$ 12,593
FCC spectrum licenses	1,687		0
Noncurrent portion of financing leases	1,627
Other	749		1,771
Other liabilities	$ 16,676	$ 16,008	$ 14,364