Acquisitions (Narrative) (Details) - USD ($) $ in Thousands			1 Months Ended	3 Months Ended		12 Months Ended
	Mar. 01, 2018	Mar. 27, 2017	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Business Acquisition [Line Items]
Acquisition holdback				$ 1,460	$ 375
Goodwill			$ 263,999	263,999		$ 261,792
Transaction costs				234	$ 273
Shone Lumber [Member]
Business Acquisition [Line Items]
Date of acquisition	Mar. 01, 2018
Purchase price	$ 22,400
Acquisition holdback	1,500
Goodwill	2,200
Accounts receivable	6,400
Inventory	8,800
Property and equipment	3,100
Current liabilities	5,200
Pre-acquisition sales						$ 70,700
Transaction costs				$ 200
Net sales of acquiree since acquisition date			5,400
Estimated pre-tax earnings of acquiree since acquisition date			$ 300
Code Plus [Member]
Business Acquisition [Line Items]
Date of acquisition		Mar. 27, 2017
Purchase price		$ 7,100
Earnout provision		800
Goodwill		3,400
Customer relationships [Member] | Shone Lumber [Member]
Business Acquisition [Line Items]
Intangible assets	$ 7,100
Useful life	9 years
Customer relationships [Member] | Code Plus [Member]
Business Acquisition [Line Items]
Intangible assets		$ 2,300
Useful life		12 years
Non-compete agreements [Member] | Code Plus [Member]
Business Acquisition [Line Items]
Intangible assets		$ 500
Useful life		5 years