Revenue Recognition - Contracts with Customer (Details)	3 Months Ended
	Mar. 31, 2018 USD ($)
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
Contract Assets
Beginning balance	0
Additions	1,556,000
Deductions	(1,556,000)
Ending balance	0
Contract Costs
Beginning balance	239,000
Additions	0
Deductions	(47,000)
Ending balance	192,000
Contract Liabilities: Deferred Revenue
Beginning balance	18,966,000
Additions	1,465,000
Deductions	(7,383,000)
Ending balance	13,048,000
Impairment charges related to contract assets	0
Change in Contract with Customer, Liability [Abstract]
Performance obligations satisfied	5,828,000
Changes in the estimated transaction price allocated to performance obligations satisfied in prior periods	0
Performance obligations satisfied from new activities in the period - contract revenue	8,214,000
Total revenue	$ 14,042,000