Segment Information - Reconciliation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Total revenue	$ 52,824	$ 56,800	$ 102,328	$ 110,853
Gross profit	26,205	29,218	51,533	55,691
Operating expenses	30,669	32,353	60,794	63,696
Other operating expenses	(12)	1,350	181	1,555
Interest and other income, net	(257)	(451)	(509)	(770)
Loss before provision for income taxes	(4,195)	(4,034)	(8,933)	(8,790)
Operating Segments \| GovDeals
Segment Reporting Information [Line Items]
Total revenue	7,822	7,697	15,837	15,355
Gross profit	7,278	7,042	14,724	14,103
Operating Segments \| RSCG
Segment Reporting Information [Line Items]
Total revenue	36,257	34,011	67,954	63,489
Gross profit	12,394	12,287	22,699	21,836
Operating Segments \| CAG
Segment Reporting Information [Line Items]
Total revenue	7,039	13,684	14,981	29,165
Gross profit	4,922	8,614	10,736	17,496
Operating Segments \| Machinio
Segment Reporting Information [Line Items]
Total revenue	1,706	1,374	3,556	2,366
Gross profit	1,611	1,265	3,374	2,143
Corporate & Other
Segment Reporting Information [Line Items]
Total revenue	0	34	0	478
Gross profit	0	10	0	113
Revenue
Segment Reporting Information [Line Items]
Total revenue	35,203	37,355	65,552	73,090
Revenue \| Operating Segments \| GovDeals
Segment Reporting Information [Line Items]
Total revenue	0	0	0	0
Revenue \| Operating Segments \| RSCG
Segment Reporting Information [Line Items]
Total revenue	32,577	29,823	60,403	55,894
Revenue \| Operating Segments \| CAG
Segment Reporting Information [Line Items]
Total revenue	2,626	7,498	5,149	16,727
Revenue \| Operating Segments \| Machinio
Segment Reporting Information [Line Items]
Total revenue	0	0	0	0
Revenue \| Corporate & Other
Segment Reporting Information [Line Items]
Total revenue	0	34	0	469
Fee revenue
Segment Reporting Information [Line Items]
Total revenue	17,621	19,445	36,776	37,763
Fee revenue \| Operating Segments \| GovDeals
Segment Reporting Information [Line Items]
Total revenue	7,822	7,697	15,837	15,355
Fee revenue \| Operating Segments \| RSCG
Segment Reporting Information [Line Items]
Total revenue	3,680	4,188	7,551	7,595
Fee revenue \| Operating Segments \| CAG
Segment Reporting Information [Line Items]
Total revenue	4,413	6,186	9,832	12,438
Fee revenue \| Operating Segments \| Machinio
Segment Reporting Information [Line Items]
Total revenue	1,706	1,374	3,556	2,366
Fee revenue \| Corporate & Other
Segment Reporting Information [Line Items]
Total revenue	$ 0	$ 0	$ 0	$ 9

Aggregate revenue less cost of goods and services sold or operating expenses directly attributable to the revenue generation activity.

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