Goodwill and Intangible Assets - Intangible Assets Subject to Amortization (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets									$ 4,993	$ 6,126	$ 6,594
Gross Carrying Amount	$ 103,446				$ 113,807				103,446	113,807
Accumulated Amortization	(94,210)				(99,668)				(94,210)	(99,668)
Total	9,236				14,139				9,236	14,139
Completed technology
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	300	$ 400	$ 500	$ 600	500	$ 500	$ 500	$ 500	1,766	1,974	2,380
Gross Carrying Amount	83,764				82,724				83,764	82,724
Accumulated Amortization	(80,136)				(77,331)				(80,136)	(77,331)
Total	3,628				5,393				$ 3,628	$ 5,393
Average Life									5 years	5 years
Customer contracts and relationships
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets									$ 2,927	$ 4,098	4,214
Gross Carrying Amount	19,332				30,583				19,332	30,583
Accumulated Amortization	(13,870)				(22,283)				(13,870)	(22,283)
Total	5,462				8,300				$ 5,462	$ 8,300
Average Life									9 years	8 years
Trade names
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets									$ 125	$ 25	0
Gross Carrying Amount	0				150				0	150
Accumulated Amortization	0				(25)				0	(25)
Total	0				125				$ 0	$ 125
Average Life									0 years	1 year
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets									$ 175	$ 29	$ 0
Gross Carrying Amount	350				350				350	350
Accumulated Amortization	(204)				(29)				(204)	(29)
Total	$ 146				$ 321				$ 146	$ 321
Average Life									2 years	2 years