Segment Reporting (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Mar. 31, 2017 USD ($) segment	Mar. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)
Segment Reporting
Number of business segments | segment			3
Segment revenue	$ 259,293	$ 202,332	$ 514,868	$ 420,750
Depreciation and amortization	(18,365)	(14,115)	(36,207)	(27,897)
Operating income (loss)	14,675	12,180	34,015	37,003
Net interest expense	(8,222)	(8,056)	(17,141)	(16,273)
Other income (expense), net	1,973	(12)	2,127	(81)
Income tax provision	(3,300)	(1,500)	(7,200)	(5,100)
Income from continuing operations	5,126	2,612	11,801	15,549
Income (loss) from discontinued operations, net of income taxes	6	(228)	159	(444)
Net income	5,132	2,384	11,960	15,105
Capital expenditures	14,193	13,197	29,733	20,882
Segment assets	1,229,637	1,238,443	1,229,637	1,238,443	$ 1,238,443
Building products
Segment Reporting
Segment revenue	140,716	98,101	275,757	199,696
Construction materials
Segment Reporting
Segment revenue	116,037	102,849	236,028	219,097
Energy technology
Segment Reporting
Segment revenue	2,540	1,382	3,083	1,957
Operating Segments | Building products
Segment Reporting
Segment revenue	140,716	98,101	275,757	199,696
Depreciation and amortization	(11,867)	(9,117)	(23,582)	(17,977)
Operating income (loss)	11,383	6,344	22,783	18,019
Capital expenditures	9,356	6,854	20,756	11,255
Segment assets	700,035	676,012	700,035	676,012
Operating Segments | Construction materials
Segment Reporting
Segment revenue	116,037	102,849	236,028	219,097
Depreciation and amortization	(5,441)	(4,523)	(10,706)	(8,963)
Operating income (loss)	15,195	13,691	33,793	34,054
Capital expenditures	4,122	5,487	7,400	7,869
Segment assets	372,932	385,595	372,932	385,595
Operating Segments | Energy technology
Segment Reporting
Segment revenue	2,540	1,382	3,083	1,957
Depreciation and amortization	(378)	(324)	(533)	(647)
Operating income (loss)	(1,489)	(1,163)	(3,302)	(2,884)
Capital expenditures	58	0	78	0
Segment assets	41,295	43,412	41,295	43,412
Corporate, Non-Segment
Segment Reporting
Segment revenue	0	0	0	0
Depreciation and amortization	(679)	(151)	(1,386)	(310)
Operating income (loss)	(10,414)	(6,692)	(19,259)	(12,186)
Capital expenditures	657	856	1,499	1,758
Segment assets	$ 115,375	$ 133,424	$ 115,375	$ 133,424