Condensed Financial Information of Registrant Balance Sheets (Detail) - USD ($) $ in Thousands		Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Current assets
Cash and cash equivalents		$ 24,683	$ 117,335
Prepaid expenses and other current assets		32,667	27,566
Total current assets		207,281	281,469
Total assets		937,331	939,611
Current liabilities
Accrued expenses		119,497	116,317
Total current liabilities		349,233	373,796
Partners’ capital		296,780	263,893	$ 263,724	$ 257,915
Total liabilities and partners’ capital		937,331	939,611
STAR GROUP, L.P.
Current assets
Cash and cash equivalents		41	40	$ 41	$ 41
Prepaid expenses and other current assets		367	343
Total current assets		408	383
Investment in subsidiaries	[1]	296,507	263,597
Total assets		296,915	263,980
Current liabilities
Accrued expenses		135	87
Total current liabilities		135	87
Partners’ capital		296,780	263,893
Total liabilities and partners’ capital		$ 296,915	$ 263,980

[1] Investments in Star Acquisitions, Inc. and subsidiaries are recorded in accordance with the equity method of accounting.