Description of Business and Summary of Significant Accounting Policies Deferred Revenue Rollforward $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Revenue Recognition and Deferred Revenue [Abstract]
Deferred Revenue, beginning of period	$ 23,985
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Deferred Revenue	14,045
Recognition of Deferred Revenue	(12,560)
Deferred Revenue, Additions	10,844
Deferred Revenue, end of period	$ 36,314