Supplemental Financial Information (Schedule of Consolidating Statements of Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Schedule Of Supplemental Financial Information [Line Items]
Net income	$ 8,352	$ 3,996
Other comprehensive income (loss):
Foreign currency translation adjustment	110	679
Cumulative effect of new accounting principle in period of adoption			$ 274
Adjustment to retirement benefit liability, net of tax	(5)	(3)
Adjustment to post employment health care benefit liability, net of tax	32	29
Other comprehensive income (loss)	(213)	705
Total comprehensive income	8,139	4,701
Guarantor Subsidiaries
Other comprehensive income (loss):
Foreign currency translation adjustment	0
Adjustment to retirement benefit liability, net of tax	(5)
Adjustment to post employment health care benefit liability, net of tax	32
Other comprehensive income (loss)	(323)
Total comprehensive income	10,647
Non-Guarantor Subsidiaries
Other comprehensive income (loss):
Foreign currency translation adjustment	110
Adjustment to retirement benefit liability, net of tax	0
Adjustment to post employment health care benefit liability, net of tax	0
Other comprehensive income (loss)	110
Total comprehensive income	1,200
Gibraltar Industries, Inc.
Other comprehensive income (loss):
Foreign currency translation adjustment	0
Adjustment to retirement benefit liability, net of tax	0
Adjustment to post employment health care benefit liability, net of tax	0
Other comprehensive income (loss)	0
Total comprehensive income	8,489
Reportable Legal Entities | Guarantor Subsidiaries
Schedule Of Supplemental Financial Information [Line Items]
Net income	10,970	6,343
Other comprehensive income (loss):
Foreign currency translation adjustment		0
Adjustment to retirement benefit liability, net of tax		(3)
Adjustment to post employment health care benefit liability, net of tax		29
Other comprehensive income (loss)		26
Total comprehensive income		6,369
Reportable Legal Entities | Non-Guarantor Subsidiaries
Schedule Of Supplemental Financial Information [Line Items]
Net income	1,090	(692)
Other comprehensive income (loss):
Foreign currency translation adjustment		679
Adjustment to retirement benefit liability, net of tax		0
Adjustment to post employment health care benefit liability, net of tax		0
Other comprehensive income (loss)		679
Total comprehensive income		(13)
Reportable Legal Entities | Gibraltar Industries, Inc.
Schedule Of Supplemental Financial Information [Line Items]
Net income	8,489	4,242
Other comprehensive income (loss):
Foreign currency translation adjustment		0
Adjustment to retirement benefit liability, net of tax		0
Adjustment to post employment health care benefit liability, net of tax		0
Other comprehensive income (loss)		0
Total comprehensive income		4,242
Eliminations
Schedule Of Supplemental Financial Information [Line Items]
Net income	(12,197)	(5,897)
Other comprehensive income (loss):
Foreign currency translation adjustment	0	0
Adjustment to retirement benefit liability, net of tax	0	0
Adjustment to post employment health care benefit liability, net of tax	0	0
Other comprehensive income (loss)	0	0
Total comprehensive income	$ (12,197)	$ (5,897)
Accounting Standards Update 2014-09
Other comprehensive income (loss):
Cumulative effect of new accounting principle in period of adoption			(350)
Accounting Standards Update 2014-09 | Guarantor Subsidiaries
Other comprehensive income (loss):
Cumulative effect of new accounting principle in period of adoption			$ (350)