Acquisitions (Narrative) (Details) - USD ($) $ in Thousands						3 Months Ended	9 Months Ended
	Sep. 16, 2019	Sep. 03, 2019	Aug. 01, 2019	Feb. 08, 2019	Jan. 14, 2019	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Business Acquisition [Line Items]
Acquisition holdback							$ 3,462	$ 4,527
Goodwill							295,390		$ 297,146
Barefoot [Member]
Business Acquisition [Line Items]
Date of acquisition					Jan. 14, 2019
Locust [Member]
Business Acquisition [Line Items]
Date of acquisition				Feb. 08, 2019
Kingston Lumber [Member]
Business Acquisition [Line Items]
Date of acquisition			Aug. 01, 2019
Heritage One [Member]
Business Acquisition [Line Items]
Date of acquisition		Sep. 03, 2019
Colorado Fasteners [Member]
Business Acquisition [Line Items]
Date of acquisition	Sep. 16, 2019
2019 Acquisitions [Member]
Business Acquisition [Line Items]
Purchase price						$ 89,500		89,500
Acquisition holdback								4,200
Payment of acquisition holdback							$ 4,200
Goodwill						19,000		19,000
Accounts receivable						22,100		22,100
Inventory						14,600		14,600
Property and equipment						5,600		5,600
Net sales of acquiree since acquisition date						38,700		84,600
Estimated pre-tax earnings of acquiree since acquisition date						2,900		7,100
Customer relationships [Member] | 2019 Acquisitions [Member]
Business Acquisition [Line Items]
Intangible assets						33,100		$ 33,100
Useful life								9 years
Non-compete agreements [Member] | 2019 Acquisitions [Member]
Business Acquisition [Line Items]
Intangible assets						$ 500		$ 500
Useful life								4 years