Significant Accounting Policies - Summary of Adopting ASC 842 on Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Oct. 01, 2019	Sep. 30, 2019
ASSETS
Operating lease right of use assets	$ 18,593
Current liabilities:
Short-term operating lease liabilities	5,270
Accrued expenses and other current liabilities	42,581		$ 24,194
Long-term operating lease liabilities	15,669
Other liabilities	$ 39,138		21,536
Stockholders' Equity:
Net parent investment			$ 1,097,127
Topic ASC 842
ASSETS
Operating lease right of use assets		$ 19,594
Current liabilities:
Short-term operating lease liabilities		4,863
Accrued expenses and other current liabilities		22,729
Long-term operating lease liabilities		16,883
Other liabilities		20,849
Stockholders' Equity:
Net parent investment		1,097,127
As Previously Reported
Current liabilities:
Accrued expenses and other current liabilities		24,194
Other liabilities		21,536
Stockholders' Equity:
Net parent investment		1,097,127
Restatement Adjustment | Topic ASC 842
ASSETS
Operating lease right of use assets		19,594
Current liabilities:
Short-term operating lease liabilities		4,863
Accrued expenses and other current liabilities		(1,465)
Long-term operating lease liabilities		16,883
Other liabilities		$ (687)