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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) |  |

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