Acquisitions (Details) (USD $)	3 Months Ended		6 Months Ended		0 Months Ended		3 Months Ended
	Mar. 31, 2015 item	Mar. 31, 2014	Mar. 31, 2015 item	Mar. 31, 2014	Dec. 12, 2013	May 16, 2014	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Acquisitions
Number of product categories in niche roofing	3		3
Estimated fair values of assets acquired and liabilities assumed
Goodwill	$ 175,512,000		$ 175,512,000					$ 175,586,000
Non-controlling interest in consolidated subsidiary
Balance			13,252,000				13,252,000
Net income attributable to non-controlling interest	259,000	236,000	504,000	230,000
Balance	12,829,000		12,829,000
Entegra
Acquisitions
Total cash consideration of acquisition					57,500,000
Fees for advisory, legal and other professional services									400,000
Estimated fair values of assets acquired and liabilities assumed
Current assets					8,261,000
Current liabilities					(3,422,000)
Property, plant and equipment					10,589,000
Goodwill					28,156,000
Net assets acquired					70,784,000
Less redeemable non-controlling interest					(13,252,000)
Net assets attributable to Headwaters					57,532,000
Intangible assets acquired:
Noncontrolling equity interest (as a percent)					20.00%
Minimum period following the acquisition date after which remaining noncontrolling equity interest may be acquired					5 years
Minimum period following the acquisition date after which the noncontrolling owners may require remaining noncontrolling equity interests to be acquired					18 months
Period over which goodwill is expected to be deductible for tax purpose					15 years
Non-controlling interest in consolidated subsidiary
Balance			13,252,000				13,252,000
Net income attributable to non-controlling interest			504,000
Dividends paid to non-controlling interest			(927,000)
Balance	12,829,000		12,829,000
Entegra | Trade Names
Intangible assets acquired:
Indefinite lived intangible assets					6,600,000
Entegra | Customer Relationships
Intangible assets acquired:
Finite lived intangible assets					20,600,000
Estimated useful lives					15 years
Roof Tile Acquisition LLC
Intangible assets acquired:
Percentage of equity interests acquired					80.00%
Gerard
Acquisitions
Total cash consideration of acquisition						27,600,000
Fees for advisory, legal and other professional services								300,000
Estimated fair values of assets acquired and liabilities assumed
Current assets						9,236,000
Current liabilities						(1,691,000)
Property, plant and equipment						8,314,000
Goodwill						7,719,000
Long-term liabilities						(3,906,000)
Net assets acquired						27,572,000
Intangible assets acquired:
Period over which goodwill is expected to be deductible for tax purpose						15 years
Gerard | Trade Names
Intangible assets acquired:
Indefinite lived intangible assets						3,900,000
Gerard | Customer Relationships
Intangible assets acquired:
Finite lived intangible assets						4,000,000
Estimated useful lives						15 years
Other Business Acquisitions
Acquisitions
Total cash consideration of acquisition							1,200,000
Intangible assets acquired:
Percentage of equity interests acquired							100.00%
Construction Materials | Other Business Acquisitions
Acquisitions
Total cash consideration of acquisition		$ 3,100,000						$ 7,400,000