Condensed Financial Information of Registrant of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Condensed Income Statements, Captions [Line Items]
Revenues	$ 181,584	$ 225,801	$ 532,052	$ 384,118	$ 162,064	$ 218,194	$ 462,025	$ 319,055	$ 1,323,555	$ 1,161,338	$ 1,674,291
General and administrative expenses									24,998	23,366	25,908
Operating income (loss)	(27,126)	(19,811)	69,032	33,237	(29,606)	(2,955)	96,319	23,646	55,332	87,404	93,613
Net interest expense									(6,775)	(7,485)	(14,059)
Amortization of debt issuance costs									(1,281)	(1,247)	(1,818)
Loss on redemption of debt											(7,345)
Net loss before equity income	(29,092)	(21,766)	66,996	31,138	(31,923)	(4,993)	94,113	21,475	47,276	78,672	70,391
Net income	$ (17,747)	$ (13,332)	$ 39,704	$ 18,275	$ (19,095)	$ (3,238)	$ 55,209	$ 12,058	26,900	44,934	37,556
STAR GROUP, L.P.
Condensed Income Statements, Captions [Line Items]
Revenues									0	0	0
General and administrative expenses									2,116	1,363	1,314
Operating income (loss)									(2,116)	(1,363)	(1,314)
Net interest expense											(10,342)
Amortization of debt issuance costs											(521)
Loss on redemption of debt											(7,345)
Net loss before equity income									(2,116)	(1,363)	(19,522)
Equity income of Star Petro Inc. and subs									29,016	46,297	57,078
Net income									$ 26,900	$ 44,934	$ 37,556