Business Acquisitions (Details) $ in Thousands		3 Months Ended		12 Months Ended
	Aug. 01, 2017 USD ($) location	Jul. 31, 2017 USD ($) segment	Jul. 31, 2016 USD ($)	Apr. 30, 2017 USD ($)	Sep. 01, 2016
Purchase price
Number of reportable segments | segment		1
Allocation of consideration for acquisitions
Goodwill		$ 423,773		$ 423,644
Adjustments/Reclassifications
Goodwill		129
As previously reported
Adjustments/Reclassifications
Contingent consideration paid out			$ 3,304
ASI | Forecast
Purchase price
Aggregate purchase price	$ 16,500
Number of locations | location	3
2017 Acquisitions
Purchase price
Aggregate purchase price				154,043
Cash consideration				149,771
Contingent consideration				4,272
Allocation of consideration for acquisitions
Cash and cash equivalents		1,558
Trade accounts and notes receivable		37,929
Inventories		16,504
Property and equipment		8,357
Other assets		657
Goodwill		37,857
Deferred tax liability		(6,011)
Liabilities assumed		(16,958)
Purchase price		154,043
Adjustments/Reclassifications
Trade accounts and notes receivable		238
Goodwill		129
Purchase price		367
Increase in total consideration paid		367
Goodwill and intangible assets
Goodwill expected to be deductible for U.S. federal income tax purposes		25,639
Other intangible assets expected to be deductible for U.S. federal income tax purposes		53,550
Goodwill nondeductible for U.S. federal income tax purposes		12,218
Other intangible assets nondeductible for U.S. federal income tax purposes		20,600
2017 Acquisitions | Tradenames
Allocation of consideration for acquisitions
Definite lived intangible assets		9,490
2017 Acquisitions | Customer relationships
Allocation of consideration for acquisitions
Definite lived intangible assets		$ 64,660
2017 Acquisitions | As previously reported
Allocation of consideration for acquisitions
Cash and cash equivalents				1,558
Trade accounts and notes receivable				37,691
Inventories				16,504
Property and equipment				8,357
Other assets				657
Goodwill				37,728
Deferred tax liability				(6,011)
Liabilities assumed				(16,958)
Purchase price				153,676
2017 Acquisitions | As previously reported | Tradenames
Allocation of consideration for acquisitions
Definite lived intangible assets				9,490
2017 Acquisitions | As previously reported | Customer relationships
Allocation of consideration for acquisitions
Definite lived intangible assets				$ 64,660
Olympia Building Supplies, LLC/Redmill, Inc.
Business Acquisitions
Outstanding common stock purchased (as a percent)					100.00%