Operations and Significant Accounting Policies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue Recognition [Abstract]
Net Commission Service Fee Revenue	50.00%
Shipping, Handling and Transportation Costs	$ 13,100	$ 13,400	$ 12,600
Allowance for doubtful accounts	2,137	2,031
Other Noncurrent Assets [Member]
Other Assets, Noncurrent [Abstract]
Field inventory	$ 52,400	$ 44,800
Promotional, Marketing and Distribution Rights [Member]
Revenue Recognition [Abstract]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	25 years