Significant Accounting Policies Deferred Revenue (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Deferred Revenue Arrangement [Line Items]
Deferred Revenue	$ 55,586,000	$ 40,020,000	$ 55,586,000	$ 40,020,000	$ 52,620,000	$ 45,760,000	$ 36,188,000	$ 26,157,000
New contracts sold	8,054,000	6,962,000	25,226,000	22,076,000
Less: reductions for revenue recognized	(5,088,000)	(3,130,000)	(15,400,000)	(8,213,000)
Deferred Revenue, Current	23,893,000	16,045,000	23,893,000	16,045,000
Deferred Revenue, Noncurrent	$ 31,693,000	$ 23,975,000	$ 31,693,000	$ 23,975,000