Supplemental Financial Information (Schedule of Consolidating Statements of Comprehensive 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 income	$ 19,503	$ 22,837	$ 8,352	$ 20,619	$ 12,769	$ 3,996	$ 50,692	$ 37,384
Other comprehensive income (loss):
Foreign currency translation adjustment	139	(1,787)	110	1,581	1,091	679	(1,538)	3,351
Cumulative effect of accounting change (see Note 2)							(350)
Adjustment to retirement benefit liability, net of tax	(5)			(2)			(15)	(8)
Adjustment to post employment health care benefit liability, net of tax	32	$ 31	$ 32	29	$ 30	$ 29	95	88
Other comprehensive income (loss)	166			1,608			(1,808)	3,431
Total comprehensive income	19,669			22,227			48,884	40,815
Reportable Legal Entities | Guarantor Subsidiaries
Schedule Of Supplemental Financial Information [Line Items]
Net income	22,149			23,211			58,637	44,356
Other comprehensive income (loss):
Foreign currency translation adjustment	0			0			0	0
Cumulative effect of accounting change (see Note 2)							(350)
Adjustment to retirement benefit liability, net of tax	(5)			(2)			(15)	(8)
Adjustment to post employment health care benefit liability, net of tax	32			29			95	88
Other comprehensive income (loss)	27			27			(270)	80
Total comprehensive income	22,176			23,238			58,367	44,436
Reportable Legal Entities | Non-Guarantor Subsidiaries
Schedule Of Supplemental Financial Information [Line Items]
Net income	888			293			3,312	(1,747)
Other comprehensive income (loss):
Foreign currency translation adjustment	139			1,581			(1,538)	3,351
Cumulative effect of accounting change (see Note 2)							0
Adjustment to retirement benefit liability, net of tax	0			0			0	0
Adjustment to post employment health care benefit liability, net of tax	0			0			0	0
Other comprehensive income (loss)	139			1,581			(1,538)	3,351
Total comprehensive income	1,027			1,874			1,774	1,604
Reportable Legal Entities | Gibraltar Industries, Inc.
Schedule Of Supplemental Financial Information [Line Items]
Net income	19,674			20,899			51,205	37,846
Other comprehensive income (loss):
Foreign currency translation adjustment	0			0			0	0
Cumulative effect of accounting change (see Note 2)							0
Adjustment to retirement benefit liability, net of tax	0			0			0	0
Adjustment to post employment health care benefit liability, net of tax	0			0			0	0
Other comprehensive income (loss)	0			0			0	0
Total comprehensive income	19,674			20,899			51,205	37,846
Eliminations
Schedule Of Supplemental Financial Information [Line Items]
Net income	(23,208)			(23,784)			(62,462)	(43,071)
Other comprehensive income (loss):
Foreign currency translation adjustment	0			0			0	0
Cumulative effect of accounting change (see Note 2)							0
Adjustment to retirement benefit liability, net of tax	0			0			0	0
Adjustment to post employment health care benefit liability, net of tax	0			0			0	0
Other comprehensive income (loss)	0			0			0	0
Total comprehensive income	$ (23,208)			$ (23,784)			$ (62,462)	$ (43,071)