Revenue Recognition Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	$ (329,000)	$ (178,000)	$ 1,900,000
Deferred revenue	700,000			$ 700,000
Deferred expenses	300,000			400,000
Decrease in retained earnings	77,338,000	71,453,000
Operating income	9,210,000	$ 9,936,000
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	(329,000)
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in retained earnings				$ 300,000
Calculated under Revenue Guidance in Effect before Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating income	$ 9,270,000