Segment Information - Schedule of Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Segment Reporting Information [Line Items]
Total revenue	$ 129,578	$ 119,875	$ 371,530	$ 358,581
Cost of goods sold (excludes depreciation and amortization)	65,742	65,110	194,790	206,220
Segment direct profit	63,836	54,764	176,740	152,360
Operating Segments
Segment Reporting Information [Line Items]
Segment direct profit	63,836	54,781	176,740	152,411
Operating Segments \| GovDeals
Segment Reporting Information [Line Items]
Total revenue	25,524	23,966	69,082	63,725
Cost of goods sold (excludes depreciation and amortization)	1,361	1,806	3,861	5,037
Segment direct profit	24,163	22,160	65,221	58,688
Operating Segments \| RSCG
Segment Reporting Information [Line Items]
Total revenue	87,820	81,544	253,040	251,917
Cost of goods sold (excludes depreciation and amortization)	62,663	62,173	185,057	197,483
Segment direct profit	25,157	19,371	67,983	54,434
Operating Segments \| CAG
Segment Reporting Information [Line Items]
Total revenue	10,794	9,161	33,054	28,604
Cost of goods sold (excludes depreciation and amortization)	1,234	701	4,461	2,695
Segment direct profit	9,560	8,460	28,593	25,909
Operating Segments \| Machinio & Software Solutions
Segment Reporting Information [Line Items]
Total revenue	5,440	5,221	16,354	14,386
Cost of goods sold (excludes depreciation and amortization)	484	431	1,411	1,006
Segment direct profit	4,956	4,790	14,943	13,380
Corporate expenses, including elimination adjustments
Segment Reporting Information [Line Items]
Segment direct profit	0	(17)	0	(51)
Purchase revenues
Segment Reporting Information [Line Items]
Total revenue	81,838	76,517	237,042	237,159
Purchase revenues \| Operating Segments \| GovDeals
Segment Reporting Information [Line Items]
Total revenue	176	120	178	684
Purchase revenues \| Operating Segments \| RSCG
Segment Reporting Information [Line Items]
Total revenue	80,365	75,269	230,320	232,405
Purchase revenues \| Operating Segments \| CAG
Segment Reporting Information [Line Items]
Total revenue	1,296	1,128	6,544	4,070
Purchase revenues \| Operating Segments \| Machinio & Software Solutions
Segment Reporting Information [Line Items]
Total revenue	0	0	0	0
Consignment and other fee revenues
Segment Reporting Information [Line Items]
Total revenue	47,740	43,358	134,488	121,422
Consignment and other fee revenues \| Operating Segments \| GovDeals
Segment Reporting Information [Line Items]
Total revenue	25,348	23,846	68,904	63,041
Consignment and other fee revenues \| Operating Segments \| RSCG
Segment Reporting Information [Line Items]
Total revenue	7,455	6,275	22,720	19,512
Consignment and other fee revenues \| Operating Segments \| CAG
Segment Reporting Information [Line Items]
Total revenue	9,498	8,033	26,510	24,533
Consignment and other fee revenues \| Operating Segments \| Machinio & Software Solutions
Segment Reporting Information [Line Items]
Total revenue	$ 5,440	$ 5,221	$ 16,354	$ 14,386