Significant Accounting Policies Deferred Revenue (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Deferred Revenue Arrangement [Line Items]
Deferred Revenue	$ 52,620,000	$ 36,188,000	$ 52,620,000	$ 36,188,000	$ 49,345,000	$ 45,760,000	$ 30,445,000	$ 26,157,000
New contracts sold	8,848,000	8,772,000	17,172,000	15,114,000
Less: reductions for revenue recognized	(5,573,000)	(3,029,000)	(10,312,000)	(5,083,000)
Deferred Revenue, Current	22,265,000	14,678,000	22,265,000	14,678,000
Deferred Revenue, Noncurrent	$ 30,355,000	$ 21,510,000	$ 30,355,000	$ 21,510,000