Condensed Financial Information of Registrant Balance Sheets (Detail) - USD ($) $ in Thousands		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Current assets
Cash and cash equivalents		$ 52,458	$ 139,188
Prepaid expenses and other current assets		26,652	27,139
Total current assets		241,241	294,858
Total assets		673,917	692,111
Current liabilities
Accrued expenses		108,449	103,855
Total current liabilities		272,333	289,922
Partners' capital		306,068	301,493	$ 289,886	$ 273,245
Total liabilities and partners' capital		673,917	692,111
STAR GROUP, L.P.
Current assets
Cash and cash equivalents		54	324	$ 324	$ 324
Prepaid expenses and other current assets		207	199
Total current assets		261	523
Investment in subsidiaries	[1]	306,016	301,368
Total assets		306,277	301,891
Current liabilities
Accrued expenses		209	398
Total current liabilities		209	398
Partners' capital		306,068	301,493
Total liabilities and partners' capital		$ 306,277	$ 301,891

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