Long-Term Debt - Schedule of Long-term Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Debt Instrument [Line Items]
Principal Amount	$ 891,562	$ 875,562
Deferred Debt Issuance Costs	(10,854)	(11,724)
Carrying Amount	880,708	863,838
Less: current portion	101,000	75,000
Long-term debt, less current portion, gross	790,562	800,562
Long-term debt, less current portion, net	779,708	788,838
Term loan A facility
Debt Instrument [Line Items]
Principal Amount	370,000	380,000
Deferred Debt Issuance Costs	(7,302)	(7,562)
Carrying Amount	362,698	372,438
Term loan B facility
Debt Instrument [Line Items]
Principal Amount	440,562	440,562
Deferred Debt Issuance Costs	(3,552)	(4,162)
Carrying Amount	437,010	436,400
Revolving facility
Debt Instrument [Line Items]
Principal Amount	81,000	55,000
Deferred Debt Issuance Costs	0	0
Carrying Amount	$ 81,000	$ 55,000