Segment Reporting - Segment Reporting (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net Sales:
Net Sales	$ 131,234	$ 116,526	$ 387,304	$ 357,771
Operating Income:
Operating income	26,971	19,707	78,293	63,014
Adjustments:
Interest expense	(2,549)	(2,988)	(7,963)	(8,966)
Losses from equity investment	(393)	(204)	(1,148)	(29)
Other (expense)/income, net	(29)	146	(256)	(633)
Income before provision for income taxes	24,000	16,661	68,926	53,386
Depreciation and Amortization
Total depreciation and amortization	11,580	12,057	32,966	35,817
Operating Segments | Wallboard
Net Sales:
Net Sales	128,101	112,796	376,739	346,466
Operating Income:
Operating income	27,551	19,992	79,702	63,402
Depreciation and Amortization
Total depreciation and amortization	11,299	11,793	32,016	34,992
Operating Segments | Other
Net Sales:
Net Sales	3,133	3,730	10,565	11,305
Operating Income:
Operating income	(580)	(285)	(1,409)	(388)
Depreciation and Amortization
Total depreciation and amortization	281	264	950	825
Adjustments
Adjustments:
Interest expense	(2,549)	(2,988)	(7,963)	(8,966)
Losses from equity investment	(393)	(204)	(1,148)	(29)
Other (expense)/income, net	$ (29)	$ 146	$ (256)	$ (633)