Condensed Financial Information of Registrant Balance Sheets (Detail) - USD ($) $ in Thousands		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Current assets
Cash and cash equivalents		$ 4,899	$ 14,531
Prepaid expenses and other current assets		36,898	35,451
Total current assets		226,830	256,737
Total assets		752,706	729,971
Current liabilities
Accrued expenses		120,839	116,436
Total current liabilities		325,557	283,188
Partners’ capital		260,840	309,785	$ 306,068	$ 301,493
Total liabilities and partners’ capital		752,706	729,971
STAR GROUP, L.P.
Current assets
Cash and cash equivalents		50	54	$ 54	$ 324
Prepaid expenses and other current assets		232	217
Total current assets		282	271
Investment in subsidiaries	[1]	260,601	309,541
Total assets		260,883	309,812
Current liabilities
Accrued expenses		43	27
Total current liabilities		43	27
Partners’ capital		260,840	309,785
Total liabilities and partners’ capital		$ 260,883	$ 309,812

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