Subsequent Event (Details) - USD ($) $ / shares in Units, $ in Thousands					7 Months Ended	12 Months Ended
	Jun. 07, 2017	Feb. 28, 2017	Sep. 27, 2016	Apr. 01, 2014	Apr. 30, 2017	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Subsequent Events
Proceeds from term loan amendment						$ 481,225
Repayments of Lines of Credit						1,011,925	$ 697,144	$ 303,099
Second amendment to First Lien Credit Agreement | Subsequent Event
Subsequent Events
Proceeds from term loan amendment	$ 577,615
Second amendment to First Lien Credit Agreement | LIBOR | Subsequent Event
Subsequent Events
Variable rate floor (as a percent)	1.00%
Margin added to variable rate (as a percent)	3.00%
Incremental First Lien Term Commitments Amendment
Subsequent Events
Repayments of Secured Debt						$ 381,225
Incremental First Lien Term Commitments Amendment | LIBOR
Subsequent Events
Variable rate floor (as a percent)			1.00%
Margin added to variable rate (as a percent)			3.50%		3.50%
First Lien Term Loan due 2021
Subsequent Events
Proceeds from term loan amendment				$ 388,050
Repayments of Secured Debt			$ 381,225
First Lien Term Loan due 2021 | Subsequent Event
Subsequent Events
Repayments of Secured Debt	$ 477,616
First Lien Term Loan due 2021 | LIBOR
Subsequent Events
Margin added to variable rate (as a percent)						3.00%
ABL Facility | Subsequent Event
Subsequent Events
Repayments of Lines of Credit	$ 94,000
Secondary offering | GMS Inc. | Selling stockholders
Subsequent Events
Shares sold		7,992,500
Price to the public (in dollars per share)		$ 29.25
Secondary offering | GMS Inc. | Selling stockholders | Subsequent Event
Subsequent Events
Shares sold	5,750,000
Price to the public (in dollars per share)	$ 33.00
Secondary offering | GMS Inc. | Affiliates of AEA
Subsequent Events
Shares sold		3,549,302
Underwriters over-allotment option | GMS Inc. | Selling stockholders
Subsequent Events
Shares sold		1,042,500
Underwriters over-allotment option | GMS Inc. | Selling stockholders | Subsequent Event
Subsequent Events
Shares sold	750,000