Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6578-128477

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6613-128477

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Acquisitions - Narrative (Details) $ in Millions		6 Months Ended
Acquisitions - Narrative (Details) $ in Millions	May 01, 2017 location	Jun. 30, 2017 USD ($)
Minneapolis-St. Paul Metropolitan Area \| Wallboard, Inc.
Business Acquisition [Line Items]
Number of branch locations \| location	2
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