Business and Basis of Presentation - Additional Information (Details) $ / shares in Units, $ in Thousands			9 Months Ended
	Jul. 02, 2018 USD ($) $ / shares shares	Jun. 08, 2018 $ / shares shares	Jun. 30, 2018 USD ($) segment $ / shares shares	Jun. 30, 2017 USD ($)	Sep. 30, 2017 $ / shares shares
Business And Basis Of Presentation [Line Items]
Number of reportable segments | segment			2
Repayments of debt			$ 64,820	$ 164,222
Common stock, authorized | shares		185,000,000	185,000,000		185,000,000
Reverse stock split ratio		2.33839
Reverse stock split description		2.33839-for-one reverse stock split of the Company’s common stock.
Reverse stock split effective date		Jun. 08, 2018
Common stock, par value | $ / shares		$ 0.01	$ 0.01		$ 0.01
Subsequent Event
Business And Basis Of Presentation [Line Items]
Extinguishment of debt, amount	$ 501,100
IPO
Business And Basis Of Presentation [Line Items]
Payments of stock issuance costs			$ 5,370
IPO | Selling, General and Administrative Expense
Business And Basis Of Presentation [Line Items]
Payments of stock issuance costs			$ 6,808
IPO | Subsequent Event
Business And Basis Of Presentation [Line Items]
Common stock, shares issued | shares	24,495,000
Initial offering price | $ / shares	$ 22.00
Net proceeds from the issuance of common stock	$ 501,172
Underwriting discounts and estimated offering expenses	$ 37,717
IPO | Subsequent Event | Third Amended and Restated Certificate of Incorporation
Business And Basis Of Presentation [Line Items]
Common stock, authorized | shares	500,000,000
Preferred Stock, Shares Authorized | shares	50,000,000
Preferred stock, par value | $ / shares	$ 0.01
IPO | Subsequent Event | MSD Partners (“MSD”) | Monitoring Agreement
Business And Basis Of Presentation [Line Items]
Termination fee paid	$ 3,438
Ownership interest in percentage	13.00%
IPO | Subsequent Event | Second Lien Credit Facility Term Loan Due 2021
Business And Basis Of Presentation [Line Items]
Repayments of debt	$ 110,000
IPO | Subsequent Event | Revolving Credit Facility
Business And Basis Of Presentation [Line Items]
Repayments of debt	55,000
IPO | Subsequent Event | First Lien Credit Facility Term Loans
Business And Basis Of Presentation [Line Items]
Repayments of debt	336,100
IPO | Subsequent Event | Kohlberg Kravis Roberts Capital Markets LLC.
Business And Basis Of Presentation [Line Items]
Expense related to underwriting services paid	5,497
IPO | Subsequent Event | Kohlberg Kravis Roberts Capital Markets LLC. | Monitoring Agreement
Business And Basis Of Presentation [Line Items]
Termination fee paid	$ 7,598
Ownership interest in percentage	55.90%