Acquisitions (Details) (USD $)	3 Months Ended								12 Months Ended										0 Months Ended	12 Months Ended				0 Months Ended		0 Months Ended	12 Months Ended				12 Months Ended			0 Months Ended	12 Months Ended			12 Months Ended		3 Months Ended
	Sep. 30, 2014 item	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2014 item	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2014 Acquisitions, 2013 and 2014	Sep. 30, 2013 Acquisitions, 2013 and 2014	Sep. 30, 2012 Acquisitions, 2013 and 2014	Sep. 30, 2013 Acquisitions, 2013 and 2014 Acquisition-related Costs	Sep. 30, 2012 Acquisitions, 2013 and 2014 Acquisition-related Costs	Sep. 30, 2013 Acquisitions, 2013 and 2014 Fair Value Adjustment to Inventory	Sep. 30, 2012 Acquisitions, 2013 and 2014 Fair Value Adjustment to Inventory	Dec. 31, 2012 Kleer Lumber, Inc.	Sep. 30, 2014 Kleer Lumber, Inc.	Sep. 30, 2013 Kleer Lumber, Inc.	Dec. 31, 2012 Kleer Lumber, Inc.	Dec. 31, 2012 Kleer Lumber, Inc. Trade Names	Dec. 31, 2012 Kleer Lumber, Inc. Customer Relationships	Dec. 31, 2012 Kleer Lumber, Inc. Customer Relationships	Dec. 12, 2013 Entegra	Sep. 30, 2014 Entegra	Dec. 12, 2013 Entegra	Dec. 12, 2012 Entegra	Dec. 12, 2013 Entegra Trade Names	Sep. 30, 2014 Entegra Customer Relationships	Dec. 12, 2013 Entegra Customer Relationships	Dec. 12, 2013 Roof Tile Acquisition LLC	May 16, 2013 Gerard	Sep. 30, 2014 Gerard item	May 16, 2013 Gerard	May 16, 2013 Gerard Trade Names	Sep. 30, 2014 Gerard Customer Relationships	May 16, 2013 Gerard Customer Relationships	Sep. 30, 2014 Other Business Acquisitions	Mar. 31, 2014 Other Business Acquisitions
Acquisition
Total cash consideration of acquisition																			$ 43,300,000							$ 57,500,000								$ 27,000,000						$ 7,400,000	$ 3,100,000
Fees for advisory, legal and other professional services															700,000	900,000					900,000						400,000								300,000
Number of primary metal profiles sold																																			7
Number of product categories in niche roofing	3								3
Estimated fair values of assets acquired and liabilities assumed
Current assets																						5,818,000						8,261,000								9,195,000
Current liabilities																						(3,093,000)						(3,422,000)								(1,869,000)
Property, plant and equipment																						4,098,000						10,589,000								8,314,000
Goodwill	175,586,000				137,198,000				175,586,000	137,198,000	116,671,000											20,527,000						28,156,000
Goodwill and intangible assets																																				7,332,000
Long-term liabilities																																				(3,906,000)
Net assets acquired																						43,250,000						70,784,000								26,966,000
Less redeemable non-controlling interest																											(13,252,000)	(13,252,000)
Net assets attributable to Headwaters																												57,532,000
Intangible assets acquired:
Finite lived intangible assets																									11,100,000							20,600,000							4,000,000
Indefinite lived intangible assets																							4,800,000							6,600,000							3,900,000
Estimated useful lives																								15 years							15 years							15 years
Period over which goodwill is expected to be deductible for tax purpose																				15 years							15 years								15 years
Percentage of equity interests acquired																													80.00%				80.00%
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
Revenue	245,921,000	223,399,000	156,512,000	165,615,000	214,985,000	197,030,000	140,988,000	149,573,000	791,447,000	702,576,000	632,787,000	47,600,000	28,600,000
Net income (loss)	16,681,000	10,893,000	(10,082,000)	(1,434,000)	10,253,000	11,016,000	(8,260,000)	(5,872,000)	16,058,000	7,137,000	(62,248,000)	5,200,000	1,600,000
Pro forma consolidated revenue and net income (loss)
Revenue												827,574,000	784,395,000	670,682,000
Net loss												19,909,000	12,387,000	(63,095,000)
Nonrecurring expense related to the fair value adjustment to acquisition-date inventory																	1,200,000	500,000
Other costs																300,000
Non-controlling interest in consolidated subsidiary
Estimated fair value as of acquisition date																											13,252,000	13,252,000
Net income attributable to non-controlling interest									(774,000)	0	0																774,000
Dividend																											(950,000)
Adjustment of estimated redemption value									176,000	0	0																(176,000)
Balance	$ 13,252,000				$ 0				$ 13,252,000	$ 0																	$ 13,252,000