Significant Accounting Policies Deferred Revenue (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Deferred Revenue Arrangement [Line Items]
Deferred Revenue	$ 67,681,000	$ 52,620,000	$ 67,681,000	$ 52,620,000	$ 63,500,000	$ 59,915,000	$ 49,345,000	$ 45,760,000
New contracts sold	11,496,000	8,848,000	21,385,000	17,172,000
Less: reductions for revenue recognized	(7,315,000)	(5,573,000)	(13,619,000)	(10,312,000)
Deferred Revenue, Current	28,795,000	22,265,000	28,795,000	22,265,000
Deferred Revenue, Noncurrent	$ 38,886,000	$ 30,355,000	$ 38,886,000	$ 30,355,000