Business - Additional Information (Details) $ / shares in Units, $ in Thousands			9 Months Ended		12 Months Ended
	Jul. 02, 2018 USD ($) $ / shares shares	Jun. 08, 2018	Sep. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2016 USD ($)	Sep. 30, 2018 USD ($) segment $ / shares shares	Dec. 31, 2016 USD ($)
Business [Line Items]
Number of reportable segments | segment					2
Repayments of debt			$ 181,617	$ 11,700	$ 1,662,625	$ 14,600
Extinguishment of debt, amount	$ 501,100
Common stock, authorized | shares			500,000,000		500,000,000
Preferred Stock, Shares Authorized | shares			50,000,000		50,000,000
Preferred stock, par value | $ / shares			$ 0.01		$ 0.01
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
IPO
Business [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
Payments of stock issuance costs					$ 5,384
IPO | Monitoring Agreement | Kohlberg Kravis Roberts Capital Markets L L C
Business [Line Items]
Ownership interest in percentage	55.90%
IPO | Third Amended and Restated Certificate of Incorporation
Business [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 | MSD Partners (“MSD”) | Monitoring Agreement
Business [Line Items]
Ownership interest in percentage	13.00%
IPO | Selling, General and Administrative Expense
Business [Line Items]
Payments of stock issuance costs					$ 6,805
IPO | Second Lien Credit Facility Term Loan Due 2021
Business [Line Items]
Repayments of debt	$ 110,000
IPO | Revolving Credit Facility
Business [Line Items]
Repayments of debt	55,000
IPO | First Lien Credit Facility Term Loans
Business [Line Items]
Repayments of debt	$ 336,100