Acquisitions - Narrative (Details) $ in Millions			9 Months Ended
	Jul. 01, 2017 location	May 01, 2017 location	Sep. 30, 2017 USD ($) acquisition
Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Number of acquisitions completed | acquisition			8
Purchase price of acquisitions			$ 74.9
Minneapolis-St. Paul Metropolitan Area | Wallboard, Inc.
Business Acquisition [Line Items]
Number of branch locations | location		2
Missouri, Illinois and Kentucky | Ceiling and Wall Supply, Inc.
Business Acquisition [Line Items]
Number of branch locations | location	5
Minimum | Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Purchase price of acquisitions			0.8
Maximum | Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Purchase price of acquisitions			$ 20.9