Supplemental Financial Information (Schedule of Condensed Consolidating Statements of Cash Flows) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Schedule Of Supplemental Financial Information [Line Items]
Net cash provided by (used in) operating activities	$ (3,803)	$ 21,720
Cash Flows from Investing Activities
Cash paid for acquisitions, net of cash acquired	0	(18,494)
Net proceeds from sale of property and equipment	2,929	12,778
Purchases of property, plant, and equipment	(3,704)	(3,274)
Net cash used in investing activities	(775)	(8,990)
Cash Flows from Financing Activities
Long-term debt payments	(400)	(400)
Purchase of treasury stock at market prices	(6,016)	(1,003)
Net proceeds from issuance of common stock	526	247
Intercompany financing	0	0
Net cash used in financing activities	(5,890)	(1,156)
Effect of exchange rate changes on cash	(1,069)	628
Net (decrease) increase in cash and cash equivalents	(11,537)	12,202
Cash and cash equivalents at beginning of year	222,280	170,177
Cash and cash equivalents at end of period	210,743	182,379
Reportable Legal Entities | Guarantor Subsidiaries
Schedule Of Supplemental Financial Information [Line Items]
Net cash provided by (used in) operating activities	884	31,687
Cash Flows from Investing Activities
Cash paid for acquisitions, net of cash acquired		(18,494)
Net proceeds from sale of property and equipment	2,864	12,627
Purchases of property, plant, and equipment	(3,564)	(3,123)
Net cash used in investing activities	(700)	(8,990)
Cash Flows from Financing Activities
Long-term debt payments	(400)	(400)
Purchase of treasury stock at market prices	0	0
Net proceeds from issuance of common stock	0	0
Intercompany financing	(10,509)	(7,280)
Net cash used in financing activities	(10,909)	(7,680)
Effect of exchange rate changes on cash	0	0
Net (decrease) increase in cash and cash equivalents	(10,725)	15,017
Cash and cash equivalents at beginning of year	192,604
Cash and cash equivalents at end of period	181,879
Reportable Legal Entities | Non-Guarantor Subsidiaries
Schedule Of Supplemental Financial Information [Line Items]
Net cash provided by (used in) operating activities	1,956	(3,327)
Cash Flows from Investing Activities
Cash paid for acquisitions, net of cash acquired		0
Net proceeds from sale of property and equipment	65	151
Purchases of property, plant, and equipment	(140)	(151)
Net cash used in investing activities	(75)	0
Cash Flows from Financing Activities
Long-term debt payments	0	0
Purchase of treasury stock at market prices	0	0
Net proceeds from issuance of common stock	0	0
Intercompany financing	(1,624)	(116)
Net cash used in financing activities	(1,624)	(116)
Effect of exchange rate changes on cash	(1,069)	628
Net (decrease) increase in cash and cash equivalents	(812)	(2,815)
Cash and cash equivalents at beginning of year	29,676
Cash and cash equivalents at end of period	28,864
Reportable Legal Entities | Gibraltar Industries, Inc.
Schedule Of Supplemental Financial Information [Line Items]
Net cash provided by (used in) operating activities	(6,643)	(6,640)
Cash Flows from Investing Activities
Cash paid for acquisitions, net of cash acquired		0
Net proceeds from sale of property and equipment	0	0
Purchases of property, plant, and equipment	0	0
Net cash used in investing activities	0	0
Cash Flows from Financing Activities
Long-term debt payments	0	0
Purchase of treasury stock at market prices	(6,016)	(1,003)
Net proceeds from issuance of common stock	526	247
Intercompany financing	12,133	7,396
Net cash used in financing activities	6,643	6,640
Effect of exchange rate changes on cash	0	0
Net (decrease) increase in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of year	0
Cash and cash equivalents at end of period	0
Eliminations
Schedule Of Supplemental Financial Information [Line Items]
Net cash provided by (used in) operating activities	0	0
Cash Flows from Investing Activities
Cash paid for acquisitions, net of cash acquired		0
Net proceeds from sale of property and equipment	0	0
Purchases of property, plant, and equipment	0	0
Net cash used in investing activities	0	0
Cash Flows from Financing Activities
Long-term debt payments	0	0
Purchase of treasury stock at market prices	0	0
Net proceeds from issuance of common stock	0	0
Intercompany financing	0	0
Net cash used in financing activities	0	0
Effect of exchange rate changes on cash	0	0
Net (decrease) increase in cash and cash equivalents	0	$ 0
Cash and cash equivalents at beginning of year	0
Cash and cash equivalents at end of period	$ 0