Supplemental Financial Information (Schedule of Consolidating Balance Sheets) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Schedule Of Supplemental Financial Information [Line Items]
Cash and cash equivalents	$ 245,413				$ 222,280	$ 208,032			$ 170,177	$ 208,032	$ 170,177
Accounts receivable, net	180,875			$ 150,307	145,385
Intercompany balances	0				0
Inventories	97,486			81,637	86,372
Other current assets	8,949				8,727
Total current assets	532,723			462,951	462,764
Property, plant, and equipment, net	93,718				97,098
Goodwill	323,321				321,074
Acquired intangibles	99,545				105,768
Other assets	4,480				4,681
Investment in subsidiaries	0				0
Total assets	1,053,787			991,572	991,385
Accounts payable	92,997				82,387
Accrued expenses	76,268			75,380	75,467
Billings in excess of cost	21,900				12,779
Current maturities of long-term debt	400				400
Total current liabilities	191,565			170,946	171,033
Long-term debt	209,809				209,621
Deferred income taxes	32,110				31,237
Other non-current liabilities	37,428				47,775
Total shareholders’ equity	582,875	$ 560,896	$ 541,955	531,993	531,719	$ 505,431	$ 481,903	$ 466,305	$ 460,880
Total liabilities and shareholders' equity	1,053,787			$ 991,572	991,385
Reportable Legal Entities | Guarantor Subsidiaries
Schedule Of Supplemental Financial Information [Line Items]
Cash and cash equivalents	213,967				192,604					182,827	143,826
Accounts receivable, net	172,952				138,903
Intercompany balances	15,885				4,166
Inventories	92,823				82,457
Other current assets	2,115				(368)
Total current assets	497,742				417,762
Property, plant, and equipment, net	90,883				93,906
Goodwill	301,070				298,258
Acquired intangibles	91,752				97,171
Other assets	4,178				4,681
Investment in subsidiaries	63,166				61,746
Total assets	1,048,791				973,524
Accounts payable	87,351				77,786
Accrued expenses	70,826				67,746
Billings in excess of cost	19,304				9,840
Current maturities of long-term debt	400				400
Total current liabilities	177,881				155,772
Long-term debt	925				1,100
Deferred income taxes	29,499				28,907
Other non-current liabilities	37,428				47,775
Total shareholders’ equity	803,058				739,970
Total liabilities and shareholders' equity	1,048,791				973,524
Reportable Legal Entities | Non-Guarantor Subsidiaries
Schedule Of Supplemental Financial Information [Line Items]
Cash and cash equivalents	31,446				29,676					25,205	26,351
Accounts receivable, net	7,923				6,482
Intercompany balances	(3,872)				(4,490)
Inventories	4,663				3,915
Other current assets	3,932				3,680
Total current assets	44,092				39,263
Property, plant, and equipment, net	2,835				3,192
Goodwill	22,251				22,816
Acquired intangibles	7,793				8,597
Other assets	302				0
Investment in subsidiaries	0				0
Total assets	77,273				73,868
Accounts payable	5,646				4,601
Accrued expenses	3,254				2,252
Billings in excess of cost	2,596				2,939
Current maturities of long-term debt	0				0
Total current liabilities	11,496				9,792
Long-term debt	0				0
Deferred income taxes	2,611				2,330
Other non-current liabilities	0				0
Total shareholders’ equity	63,166				61,746
Total liabilities and shareholders' equity	77,273				73,868
Reportable Legal Entities | Gibraltar Industries, Inc.
Schedule Of Supplemental Financial Information [Line Items]
Cash and cash equivalents	0				0					0	0
Accounts receivable, net	0				0
Intercompany balances	(12,013)				324
Inventories	0				0
Other current assets	2,902				5,415
Total current assets	(9,111)				5,739
Property, plant, and equipment, net	0				0
Goodwill	0				0
Acquired intangibles	0				0
Other assets	0				0
Investment in subsidiaries	803,058				739,970
Total assets	793,947				745,709
Accounts payable	0				0
Accrued expenses	2,188				5,469
Billings in excess of cost	0				0
Current maturities of long-term debt	0				0
Total current liabilities	2,188				5,469
Long-term debt	208,884				208,521
Deferred income taxes	0				0
Other non-current liabilities	0				0
Total shareholders’ equity	582,875				531,719
Total liabilities and shareholders' equity	793,947				745,709
Eliminations
Schedule Of Supplemental Financial Information [Line Items]
Cash and cash equivalents	0				0					$ 0	$ 0
Accounts receivable, net	0				0
Intercompany balances	0				0
Inventories	0				0
Other current assets	0				0
Total current assets	0				0
Property, plant, and equipment, net	0				0
Goodwill	0				0
Acquired intangibles	0				0
Other assets	0				0
Investment in subsidiaries	(866,224)				(801,716)
Total assets	(866,224)				(801,716)
Accounts payable	0				0
Accrued expenses	0				0
Billings in excess of cost					0
Current maturities of long-term debt	0				0
Total current liabilities	0				0
Long-term debt	0				0
Deferred income taxes	0				0
Other non-current liabilities	0				0
Total shareholders’ equity	(866,224)				(801,716)
Total liabilities and shareholders' equity	$ (866,224)				$ (801,716)