Summary of Significant Accounting Policies - Leases (Details) - USD ($) $ in Thousands	Oct. 01, 2019	Sep. 30, 2020	Sep. 30, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liability		$ 36,437
Operating lease right of use assets		$ 34,663	$ 0
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201602Member
Deferred rent payable, net of current portion			$ 1,620
ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liability	$ 39,746
Operating lease right of use assets	38,126
Deferred rent payable, net of current portion	$ 1,620