Selected Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																9 Months Ended	12 Months Ended
	Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2018	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2016
Quarterly Financial Information Disclosure [Abstract]
Sales	$ 229,618		$ 327,354		$ 684,031		$ 436,834		$ 181,584		$ 225,801		$ 532,052		$ 384,118			$ 1,677,837		$ 1,323,555		$ 1,161,338
Gross profit for product, installation and service	43,387		79,377		216,079		124,499		42,467		63,309		184,685		118,038			463,342		408,499
Operating income (loss)	(41,654)		(8,817)		85,473		31,066		(27,126)		(19,811)		69,032		33,237			66,068		55,332		87,404
Income (loss) before income taxes	(36,925)		(11,421)		82,783		28,670		(29,092)		(21,766)		66,996		31,138		$ 34,400	63,107		47,276		78,672
Net income (loss)	(21,450)		(8,005)		54,778		30,182		(17,747)		(13,332)		39,704		18,275			55,505		26,900		44,934
Limited Partner interest in net income (loss)	$ (21,319)		$ (7,956)		$ 54,459		$ 30,007		$ (17,644)		$ (13,253)		$ 39,471		$ 18,170			$ 55,191		$ 26,744		$ 44,682
Net income (loss) per Limited Partner unit:
Basic and diluted	$ (0.40)	[1]	$ (0.15)	[1]	$ 0.81	[1]	$ 0.45	[1]	$ (0.32)	[1]	$ (0.24)	[1]	$ 0.59	[1]	$ 0.28	[1]		$ 0.89	[1],[2]	$ 0.46	[1],[2]	$ 0.70	[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 18 - Earnings Per Limited Partner Units.