Supplemental Financial Information (Schedule of Consolidating Balance Sheets) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Sep. 30, 2016	Dec. 31, 2015
Schedule Of Supplemental Financial Information [Line Items]
Cash and cash equivalents	$ 200,741		$ 222,280	$ 160,901	$ 170,177
Accounts receivable, net	145,182	$ 150,307	145,385
Intercompany balances	0		0
Inventories	90,236	81,637	86,372
Other current assets	6,712		8,727
Total current assets	442,871	462,951	462,764
Property, plant, and equipment, net	93,671		97,098
Goodwill	321,772		321,074
Acquired intangibles	104,059		105,768
Other assets	4,770		4,681
Investment in subsidiaries	0		0
Total assets	967,143	991,572	991,385
Accounts payable	80,691		82,387
Accrued expenses	53,254	75,380	75,467
Billings in excess of cost	11,572		12,779
Current maturities of long-term debt	400		400
Total current liabilities	145,917	170,946	171,033
Long-term debt	209,817		209,621
Deferred income taxes	31,339		31,237
Other non-current liabilities	38,115		47,775
Total shareholders’ equity	541,955	531,993	531,719
Total liabilities and shareholders' equity	967,143	$ 991,572	991,385
Reportable Legal Entities | Guarantor Subsidiaries
Schedule Of Supplemental Financial Information [Line Items]
Cash and cash equivalents	172,930		192,604	138,763	143,826
Accounts receivable, net	139,143		138,903
Intercompany balances	3,362		4,166
Inventories	86,265		82,457
Other current assets	2,114		(368)
Total current assets	403,814		417,762
Property, plant, and equipment, net	90,625		93,906
Goodwill	298,258		298,258
Acquired intangibles	95,275		97,171
Other assets	4,770		4,681
Investment in subsidiaries	62,594		61,746
Total assets	955,336		973,524
Accounts payable	76,994		77,786
Accrued expenses	49,631		67,746
Billings in excess of cost	9,280		9,840
Current maturities of long-term debt	400		400
Total current liabilities	136,305		155,772
Long-term debt	1,175		1,100
Deferred income taxes	28,918		28,907
Other non-current liabilities	38,115		47,775
Total shareholders’ equity	750,823		739,970
Total liabilities and shareholders' equity	955,336		973,524
Reportable Legal Entities | Non-Guarantor Subsidiaries
Schedule Of Supplemental Financial Information [Line Items]
Cash and cash equivalents	27,811		29,676	22,138	26,351
Accounts receivable, net	6,039		6,482
Intercompany balances	(4,276)		(4,490)
Inventories	3,971		3,915
Other current assets	3,550		3,680
Total current assets	37,095		39,263
Property, plant, and equipment, net	3,046		3,192
Goodwill	23,514		22,816
Acquired intangibles	8,784		8,597
Other assets	0		0
Investment in subsidiaries	0		0
Total assets	72,439		73,868
Accounts payable	3,697		4,601
Accrued expenses	1,435		2,252
Billings in excess of cost	2,292		2,939
Current maturities of long-term debt	0		0
Total current liabilities	7,424		9,792
Long-term debt	0		0
Deferred income taxes	2,421		2,330
Other non-current liabilities	0		0
Total shareholders’ equity	62,594		61,746
Total liabilities and shareholders' equity	72,439		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	914		324
Inventories	0		0
Other current assets	1,048		5,415
Total current assets	1,962		5,739
Property, plant, and equipment, net	0		0
Goodwill	0		0
Acquired intangibles	0		0
Other assets	0		0
Investment in subsidiaries	750,823		739,970
Total assets	752,785		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	208,642		208,521
Deferred income taxes	0		0
Other non-current liabilities	0		0
Total shareholders’ equity	541,955		531,719
Total liabilities and shareholders' equity	752,785		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	(813,417)		(801,716)
Total assets	(813,417)		(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	(813,417)		(801,716)
Total liabilities and shareholders' equity	$ (813,417)		$ (801,716)