Income Taxes - Components of Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Current federal			$ 57	$ 0	$ 0
Current state			512	859	595
Deferred federal			102,082	1,625	5,574
Deferred state			(8,167)	212	10,329
Total			$ 94,484	2,696	16,498
Income Tax Contingency [Line Items]
Document Fiscal Year Focus			2018
State and Local Jurisdiction
Income Tax Contingency [Line Items]
Valuation allowances and reserves, adjustments	$ 27,400	$ 8,600		$ 3,500	$ 8,600