Revenue Recognition - Contracts with Customer (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Movement in Deferred Revenue [Roll Forward]
Deferred Revenue, balance at December 31, 2017		$ 13,793,000
Changes in estimated consideration		0
Unsatisfied performance obligations		5,173,000
Deferred Revenue, balance at January 1, 2018	$ 18,966,000	18,966,000
Contract Assets
January 1, 2018 balance		0
Additions		3,047,000
Deductions		(2,493,000)
Ending balance	554,000	554,000
Contract Costs
January 1, 2018 balance		239,000
Additions		0
Deductions		(80,000)
Ending balance	159,000	159,000
Contract Liabilities: Deferred Revenue
January 1, 2018 balance		18,966,000
Additions		1,965,000
Deductions		(11,477,000)
Ending balance	9,454,000	9,454,000
Impairment charges related to contract assets		0
Change in Contract with Customer, Liability [Abstract]
Performance obligations satisfied	2,994,000	8,822,000
Changes in the estimated transaction price allocated to performance obligations satisfied in prior periods	64,000	64,000
Performance obligations satisfied from new activities in the period - contract revenue	10,480,000	18,694,000
Total revenue	$ 13,538,000	$ 27,580,000