Valuation and Qualifying Accounts (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Reserves for sales discounts	$ 15,652	$ 13,488
Inventory obsolescence reserves	$ 6,932	7,262
Inventory usage period	3 years
Inventory reserve percentage	100.00%
Product warranty accrual period of expenses used in calculation	12 months
Product warranty accrual period for sales used in calculation	12 months
Warranty	$ 5,335	$ 5,262
Parts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Product warranty period	90 days
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Sales discount percentage of customers who qualify for each program that discount available	85.00%
Product warranty accrual lag period	90 days
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Sales discount percentage of customers who qualify for each program that discount available	95.00%
Product warranty accrual lag period	6 months
Maximum | Wholegood Units
Accounts, Notes, Loans and Financing Receivable [Line Items]
Product warranty period	1 year