Income Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Contingency [Line Items]
Federal net operating loss carryforwards	$ 132,200
State net operating loss carryforwards	42,300
Alternative minimum tax credit	4,600
General business credits	32,700
Income tax receivable	4,935	$ 0
(Benefit) expense from income taxes	(37,217)	94,484	$ 2,696
Decrease in valuation allowance	0	(27,370)	(3,482)
Pre-tax income required to realize deferred tax assets prior to expiration	944,000
Deferred tax asset valuation allowance	38,486	34,212
Unrecognized tax benefits	3,473	3,494	3,804	$ 4,541
Uncertain tax positions to be reserved within twelve months	$ 32
State and Local Jurisdiction
Income Tax Contingency [Line Items]
Valuation allowances and reserves, adjustments		$ 27,400	$ 3,500