Acquisitions (Details) $ in Thousands			1 Months Ended	3 Months Ended			6 Months Ended		12 Months Ended
	Aug. 19, 2016 USD ($)	Mar. 17, 2016 USD ($)	Dec. 03, 2015 USD ($) item	Mar. 31, 2017 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Nov. 13, 2015	Sep. 30, 2014
Acquisitions
Consideration paid net of cash acquired							$ 10,530	$ 96,457
Estimated fair values of assets acquired and liabilities assumed
Goodwill				$ 300,265			300,265		$ 290,503
Intangible assets acquired:
Income tax expense (benefit)				3,300		$ 1,500	7,200	5,100
Non-controlling interest in consolidated subsidiary
Balance							13,363
Net income attributable to non-controlling interest				591		283	752	$ 579
Dividends paid to non-controlling interest							(657)
Balance				13,458			13,458		13,363
Entegra
Acquisitions
Percentage of equity interests acquired											80.00%
Intangible assets acquired:
Noncontrolling equity interest (as a percent)											20.00%
Roofing Businesses
Acquisitions
Number of acquisitions aggregated | item			2
Consideration paid net of cash acquired			$ 57,000
Estimated fair values of assets acquired and liabilities assumed
Current assets			7,402
Current liabilities			(1,565)
Property, plant and equipment			3,138
Goodwill			34,284
Long-term liabilities			(4,761)
Net assets acquired			$ 56,995
Intangible assets acquired:
Period over which goodwill is expected to be deductible for tax purpose			15 years
Roofing Businesses | Trade names
Intangible assets acquired:
Indefinite lived intangible assets			$ 4,801
Roofing Businesses | Customer relationships
Intangible assets acquired:
Finite lived intangible assets			$ 3,670
Estimated useful lives of the identified intangible assets			12 years
Roofing Businesses | Intellectual property
Intangible assets acquired:
Finite lived intangible assets			$ 10,026
Estimated useful lives of the identified intangible assets			20 years
Metro Roof Products
Acquisitions
Percentage of equity interests acquired										100.00%
SynMat
Acquisitions
Percentage of equity interests acquired		100.00%
Consideration paid net of cash acquired		$ 33,200
Future estimated consideration payments accrued		12,000
Payments of deferred consideration				5,000
Estimated fair values of assets acquired and liabilities assumed
Current assets		3,965
Current liabilities		(1,515)
Property, plant and equipment		3,710
Goodwill		4,988
Net assets acquired		$ 33,168
Intangible assets acquired:
Period over which goodwill is expected to be deductible for tax purpose		15 years
SynMat | Trade names
Intangible assets acquired:
Indefinite lived intangible assets		$ 3,900
SynMat | Contracts
Intangible assets acquired:
Finite lived intangible assets		$ 15,430
Estimated useful lives of the identified intangible assets		20 years
SynMat | Customer relationships
Intangible assets acquired:
Finite lived intangible assets		$ 2,690
Estimated useful lives of the identified intangible assets		15 years
Krestmark Industries
Acquisitions
Total cash consideration of acquisition	$ 240,100
Estimated fair values of assets acquired and liabilities assumed
Current assets	20,731
Current liabilities	(3,884)
Property, plant and equipment	5,597
Goodwill	69,309
Net assets acquired	$ 240,063
Intangible assets acquired:
Period over which goodwill is expected to be deductible for tax purpose	15 years
Prepaid compensation for employee retention obligations	$ 4,600
Krestmark Industries | Maximum
Intangible assets acquired:
Amortization period for prepaid compensation	2 years
Krestmark Industries | Trade names
Intangible assets acquired:
Indefinite lived intangible assets	$ 36,600
Krestmark Industries | Customer relationships
Intangible assets acquired:
Finite lived intangible assets	$ 109,300
Estimated useful lives of the identified intangible assets	20 years
Krestmark Industries | Non-competition agreements
Intangible assets acquired:
Finite lived intangible assets	$ 2,410
Estimated useful lives of the identified intangible assets	7 years
Decking Manufacturing Assets
Acquisitions
Total cash consideration of acquisition						$ 6,300
Concrete Roof Tile Business
Acquisitions
Total cash consideration of acquisition					$ 10,400
Intangible assets acquired:
Income tax expense (benefit)									2,000
Concrete Roof Tile Business | Other Income
Intangible assets acquired:
Gain on acquired assets held for sale							$ 1,900		$ 4,500
Windows Company
Acquisitions
Total cash consideration of acquisition				$ 5,900