SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Description
Balance at beginning of year	$ 4,201	$ 4,302	$ 4,446
Additions charged to expense	10,247	9,321	9,544
Deductions	9,258	9,422	9,688
Balance at End of Year	5,190	4,201	4,302
Reserve for bad debts
Description
Balance at beginning of year	1,225	1,410	1,300
Additions charged to expense	27		267
Reductions credited to expense		(166)
Deductions	55	19	157
Balance at End of Year	1,197	1,225	1,410
Reserve for cash discounts
Description
Balance at beginning of year	659	815	668
Additions charged to expense	9,268	9,247	9,678
Deductions	9,203	9,403	9,531
Balance at End of Year	724	659	815
Deferred tax asset valuation
Description
Balance at beginning of year	2,317	2,077	2,478
Additions charged to expense	952	240
Reductions credited to expense			(401)
Balance at End of Year	$ 3,269	$ 2,317	$ 2,077