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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
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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	Jun. 30, 2018 USD ($) acquisition	Feb. 01, 2018 branch
Business Acquisition [Line Items]
Number of acquisitions \| acquisition	2
Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Purchase price of acquisitions \| $	$ 21.9
Minnesota, North Dakota, South Dakota and Nebraska \| ArmCom Distributing Company
Business Acquisition [Line Items]
Number of branch locations		5
Wentzville and Herculaneum, Missouri \| R M Supply, Inc.
Business Acquisition [Line Items]
Number of branch locations		2