Selected Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																9 Months Ended	12 Months Ended
	Sep. 30, 2020		Jun. 30, 2020	Mar. 31, 2020		Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2020		Sep. 30, 2019		Sep. 30, 2018
Quarterly Financial Information Disclosure [Abstract]
Sales	$ 183,295		$ 232,155	$ 543,063		$ 508,945		$ 235,887		$ 283,376		$ 699,582		$ 535,027				$ 1,467,458		$ 1,753,872		$ 1,677,837
Gross profit for product, installation and service	46,818		84,159	196,440		147,603		48,482		66,191		218,549		154,484				475,020		487,706
Operating income (loss)	(36,098)		498	86,117		42,451		(43,782)		(29,933)		105,002		6,063				92,968		37,350		66,068
Income (loss) before income taxes	(44,051)		(2,051)	83,108		39,537		(46,545)		(33,153)		101,564		3,288		$ 28,700	$ 34,400	76,543		25,154		63,107
Net income (loss)	(30,199)		(46)	58,408		27,755		(33,905)		(23,098)		72,325		2,315				55,918		17,637		55,505
Limited Partners’ interest in net income	$ (29,976)		$ (45)	$ 57,999		$ 27,563		$ (33,681)		$ (22,948)		$ 71,871		$ 2,300				$ 55,541		$ 17,542		$ 55,191
Net income (loss) per Limited Partner unit:
Basic and diluted income per Limited Partner Unit:	$ (0.68)	[1]		$ 1.03	[1]	$ 0.49	[1]	$ (0.69)	[1]	$ (0.46)	[1]	$ 1.15	[1]	$ 0.04	[1]			$ 1.07	[1],[2]	$ 0.35	[1],[2]	$ 0.89	[2]

[1] The sum of the quarters do not add-up to the total due to the weighting of Limited Partner Units outstanding, rounding or the theoretical effects of FASB ASC 260-10-45-60 to Master Limited Partners earnings per unit.

[2] See Note 19 - Earnings Per Limited Partner Units.