Significant Accounting Policies Deferred Revenue (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Deferred Revenue Arrangement [Line Items]
Deferred Revenue	$ 49,345,000	$ 30,445,000	$ 45,760,000	$ 26,157,000
New contracts sold	8,324,000	6,342,000
Less: reductions for revenue recognized	(4,739,000)	(2,054,000)
Deferred Revenue, Current	20,510,000	12,569,000
Deferred Revenue, Noncurrent	$ 28,835,000	$ 17,876,000