Acquisitions (Narrative) (Details) - USD ($) $ in Thousands				1 Months Ended	3 Months Ended		12 Months Ended
	Feb. 08, 2019	Jan. 14, 2019	Mar. 01, 2018	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Business Acquisition [Line Items]
Acquisition holdback					$ 2,500	$ 1,460
Goodwill					275,845		$ 262,997
Transaction costs					580	$ 234
Barefoot [Member]
Business Acquisition [Line Items]
Date of acquisition		Jan. 14, 2019
Locust [Member]
Business Acquisition [Line Items]
Date of acquisition	Feb. 08, 2019
Barefoot And Locust [Member]
Business Acquisition [Line Items]
Purchase price					54,500
Acquisition holdback					2,500
Goodwill					12,800
Accounts receivable					12,100
Inventory					7,500
Property and equipment					2,300
Pre-acquisition sales							$ 105,000
Transaction costs					300
Net sales of acquiree since acquisition date					18,200
Estimated pre-tax earnings of acquiree since acquisition date					1,900
Shone Lumber [Member]
Business Acquisition [Line Items]
Date of acquisition			Mar. 01, 2018
Purchase price			$ 22,400
Payment of acquisition holdback					1,400
Goodwill			2,500
Accounts receivable			6,400
Inventory			8,800
Property and equipment			2,900
Current liabilities			5,300
Net sales of acquiree since acquisition date				$ 5,400
Estimated pre-tax earnings of acquiree since acquisition date				$ 300
Customer relationships [Member] | Barefoot And Locust [Member]
Business Acquisition [Line Items]
Intangible assets					$ 23,300
Useful life					9 years
Customer relationships [Member] | Shone Lumber [Member]
Business Acquisition [Line Items]
Intangible assets			$ 7,000
Useful life			9 years
Non-compete agreements [Member] | Barefoot And Locust [Member]
Business Acquisition [Line Items]
Intangible assets					$ 200
Useful life					2 years