Income Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Tax Contingency [Line Items]
Expense (benefit) from income taxes	$ 17,973	$ (37,217)	$ 94,484
Federal net operating loss carryforwards	120,000
State net operating loss carryforwards	42,800
General business credits	33,600
Alternative minimum tax credit		4,600
Income tax, refund claim		4,600
Decrease in valuation allowance	0	0	(27,370)
Pre-tax income required to realize deferred tax assets prior to expiration	915,500
Deferred tax asset valuation allowance	39,185	38,486
Unrecognized tax benefits	3,441	3,473	$ 3,494	$ 3,804
Uncertain tax positions to be reserved within twelve months	83
Income Tax Credits and Adjustments	$ 9,200	$ 9,200