Acquisitions (Narrative) (Details) - USD ($) $ in Thousands			3 Months Ended		6 Months Ended		12 Months Ended
	Apr. 03, 2017	Mar. 27, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Business Acquisition [Line Items]
Goodwill			$ 262,077		$ 262,077		$ 254,832
Acquisition costs			44	$ 0	317	$ 0
Code Plus [Member]
Business Acquisition [Line Items]
Date of acquisition		Mar. 27, 2017
Purchase price		$ 7,100
Initial holdback		400
Earnout provision		800
Goodwill		3,400
Pre-acquisition sales							14,200
Goodwill recognized expected to be deductible for tax		3,400
TexPly [Member]
Business Acquisition [Line Items]
Date of acquisition	Apr. 03, 2017
Purchase price	$ 32,000
Escrow Deposit Related to Property Acquisition	2,500
Goodwill	3,800
Pre-acquisition sales							$ 55,200
Goodwill recognized expected to be deductible for tax	3,800
Accounts receivable	5,200
Inventories	4,000
Property and equipment	5,400
Code Plus and TexPly [Member]
Business Acquisition [Line Items]
Net sales of acquiree since acquisition date			19,200		19,500
Earnings of acquiree since acquisition date			1,100		1,100
Customer relationships [Member] | Code Plus [Member]
Business Acquisition [Line Items]
Goodwill adjustment in period			1,100
Intangible assets		$ 2,300
Useful life		12 years
Customer relationships [Member] | TexPly [Member]
Business Acquisition [Line Items]
Intangible assets	$ 13,400
Useful life	13 years
Non-compete agreements [Member] | Code Plus [Member]
Business Acquisition [Line Items]
Intangible assets		$ 500
Useful life		5 years
Selling, general and administrative expenses [Member] | Code Plus [Member]
Business Acquisition [Line Items]
Acquisition costs			0		100
Selling, general and administrative expenses [Member] | TexPly [Member]
Business Acquisition [Line Items]
Acquisition costs			$ 0		$ 200