Supplemental Financial Information (Schedule of Consolidating Statements of Income) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Schedule Of Supplemental Financial Information [Line Items]
Net sales:	$ 280,086			$ 274,574			$ 761,459	$ 728,806
Cost of sales	209,807			205,839			572,359	548,991
Gross profit	70,279			68,735			189,100	179,815
Selling, general, and administrative expense	40,875			33,042			113,579	109,513
Income from operations	29,404			35,693			75,521	70,302
Interest expense (income)	2,906			3,486			9,305	10,612
Other expense (income)	522			404			(50)	811
Income before taxes	25,976			31,803			66,266	58,879
Provision for income taxes	6,473			11,184			15,574	21,090
Income from continuing operations	19,503			20,619			50,692	37,789
Loss before taxes	0			0			0	(644)
Benefit of income taxes	0			0			0	(239)
Loss from discontinued operations	0			0			0	(405)
Equity in earnings from subsidiaries	0			0			0	0
Net income	19,503	$ 22,837	$ 8,352	20,619	$ 12,769	$ 3,996	50,692	37,384
Reportable Legal Entities | Guarantor Subsidiaries
Schedule Of Supplemental Financial Information [Line Items]
Net sales:	268,302			264,448			729,256	700,848
Cost of sales	200,725			198,103			548,391	527,389
Gross profit	67,577			66,345			180,865	173,459
Selling, general, and administrative expense	39,466			31,003			108,639	101,190
Income from operations	28,111			35,342			72,226	72,269
Interest expense (income)	(427)			105			(724)	459
Other expense (income)	95			100			234	345
Income before taxes	28,443			35,137			72,716	71,465
Provision for income taxes	7,182			12,219			17,391	24,957
Income from continuing operations								46,508
Loss before taxes								(644)
Benefit of income taxes								(239)
Loss from discontinued operations								(405)
Equity in earnings from subsidiaries	888			293			3,312	(1,747)
Net income	22,149			23,211			58,637	44,356
Reportable Legal Entities | Non-Guarantor Subsidiaries
Schedule Of Supplemental Financial Information [Line Items]
Net sales:	19,211			15,514			45,735	37,383
Cost of sales	16,338			12,844			36,987	30,565
Gross profit	2,873			2,670			8,748	6,818
Selling, general, and administrative expense	1,374			2,005			4,825	8,212
Income from operations	1,499			665			3,923	(1,394)
Interest expense (income)	(70)			(21)			(178)	(54)
Other expense (income)	427			304			(284)	466
Income before taxes	1,142			382			4,385	(1,806)
Provision for income taxes	254			89			1,073	(59)
Income from continuing operations								(1,747)
Loss before taxes								0
Benefit of income taxes								0
Loss from discontinued operations								0
Equity in earnings from subsidiaries	0			0			0	0
Net income	888			293			3,312	(1,747)
Reportable Legal Entities | Gibraltar Industries, Inc.
Schedule Of Supplemental Financial Information [Line Items]
Net sales:	0			0			0	0
Cost of sales	0			0			0	0
Gross profit	0			0			0	0
Selling, general, and administrative expense	35			34			115	111
Income from operations	(35)			(34)			(115)	(111)
Interest expense (income)	3,403			3,402			10,207	10,207
Other expense (income)	0			0			0	0
Income before taxes	(3,438)			(3,436)			(10,322)	(10,318)
Provision for income taxes	(963)			(1,124)			(2,890)	(3,808)
Income from continuing operations								(6,510)
Loss before taxes								0
Benefit of income taxes								0
Loss from discontinued operations								0
Equity in earnings from subsidiaries	22,149			23,211			58,637	44,356
Net income	19,674			20,899			51,205	37,846
Eliminations
Schedule Of Supplemental Financial Information [Line Items]
Net sales:	(7,427)			(5,388)			(13,532)	(9,425)
Cost of sales	(7,256)			(5,108)			(13,019)	(8,963)
Gross profit	(171)			(280)			(513)	(462)
Selling, general, and administrative expense	0			0			0	0
Income from operations	(171)			(280)			(513)	(462)
Interest expense (income)	0			0			0	0
Other expense (income)	0			0			0	0
Income before taxes	(171)			(280)			(513)	(462)
Provision for income taxes	0			0			0	0
Income from continuing operations								(462)
Loss before taxes								0
Benefit of income taxes								0
Loss from discontinued operations								0
Equity in earnings from subsidiaries	(23,037)			(23,504)			(61,949)	(42,609)
Net income	$ (23,208)			$ (23,784)			$ (62,462)	$ (43,071)