Senior Notes - Additional Information (Details)	Jul. 14, 2010 USD ($) Contract	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	May 08, 2018 USD ($)
Debt Disclosure [Line Items]
Debt Issuance Costs, Net		$ 5,200,000	$ 6,100,000
July 2010 Senior Notes
Debt Disclosure [Line Items]
Senior Notes issued in a private placement to a group of institutional investors	$ 245,000,000
Number of series of Senior Notes issued | Contract	4
Debt Instrument, Covenant, Leverage Ratio, Maximum	3.00
Debt Instrument, Covenant, Fixed Charge Coverage Ratio, Minimum	2.50
May 2018 Senior Notes
Debt Disclosure [Line Items]
Senior Notes issued in a private placement to a group of institutional investors				$ 400,000,000