Income Taxes - Components of Income Tax Provision (Details) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Current:
Federal				$ 431	$ (26)	$ 1,043
State and foreign				704	9,288	6,233
Total				1,135	9,262	7,276
Deferred:
Federal				(4,264)	9,498	4,082
State and foreign				5,535	(371)	(265)
Total				1,271	9,127	3,817
Total income tax expense	$ (1,058)		$ 7,411	$ 2,406	18,389	$ 11,093
Charge resulting from remeasured deferred tax asset		$ 1,900	$ 2,800		2,100
Charge resulting from recording valuation allowance not likely to be utilized					$ 2,600