Income Taxes - Differences Between Income Tax Provision (Benefit) and Income Taxes Computed using Applicable U.S. Statutory Federal Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Differences between the income tax provision (benefit) and income taxes computed using the applicable U.S. statutory federal tax rate
Income tax provision computed at federal statutory rate	$ 1,983	$ 5,014	$ 4,923
State income taxes, net of federal benefit	(630)	692	137
Foreign income taxed at different rates	550	920	(1,644)
Impact of investments in subsidiaries	(536)	(729)	(965)
Change in deferred tax asset valuation allowance	(2,264)	(75,918)	319
Net increase (reduction) in uncertain tax positions	720	220	731
Global intangible low taxed income, net of foreign tax credits	942
Impact of U.S. federal tax rate change		15,287
Compensation	(1,103)	(701)	579
Tax credits	(2,741)	(1,633)	(1,151)
Merger costs	572	1,405
Other taxes	764	70	98
Non-deductible expenses	174	176	220
Transition tax	2,836	8,027
Deferred state rate change due to acquisition	(1,360)
Other	(18)	(81)	133
Income tax provision (benefit)	$ (111)	$ (47,251)	$ 3,380