Condensed Consolidating Financial Information - Consolidating Balance Sheet (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Current assets:
Cash	$ 34,010	$ 13,862	$ 12,162	$ 49,537
Accounts receivable, net of allowance	203,340	164,317
Inventories	199,549	174,378
Prepaid expenses and other current assets	25,092	12,141
Deferred income taxes	31,760	33,465
Income tax receivable, net	2,147	1,300
Total current assets	495,898	399,463
Property, plant and equipment, net	75,330	71,127
Investment in joint venture	2,168	2,972
Investment in subsidiaries
Intercompany accounts
Goodwill	4,399	4,399
Intangible assets, net	787	839
Deferred income taxes	6,826	6,138
Other noncurrent assets	16,794	17,755
Total assets	602,202	502,693
Current liabilities:
Accounts payable	106,981	81,577
Accrued liabilities	52,685	48,424
Accrued interest	3,395	3,287
Income taxes payable	334	248
Total current liabilities	163,395	133,536
Long-term debt	431,000	389,522
Other noncurrent liabilities	27,678	27,436
Obligations and advances in excess of investment in subsidiary
Intercompany accounts
Total liabilities	622,073	550,494
Commitments and contingencies
Global Brass and Copper Holdings, Inc. stockholder's (deficit) / equity	(23,647)	(51,351)
Noncontrolling interest	3,776	3,550
Total (deficit) / equity	(19,871)	(47,801)	(65,951)	82,660
Total liabilities and (deficit) / equity	602,202	502,693
Parent [Member]
Current assets:
Cash
Accounts receivable, net of allowance
Inventories
Prepaid expenses and other current assets
Deferred income taxes
Income tax receivable, net
Total current assets
Property, plant and equipment, net
Investment in joint venture
Investment in subsidiaries
Intercompany accounts
Goodwill
Intangible assets, net
Deferred income taxes
Other noncurrent assets
Total assets
Current liabilities:
Accounts payable
Accrued liabilities
Accrued interest
Income taxes payable
Total current liabilities
Long-term debt
Other noncurrent liabilities
Obligations and advances in excess of investment in subsidiary	16,502	42,522
Intercompany accounts	7,145	8,829
Total liabilities	23,647	51,351
Commitments and contingencies
Global Brass and Copper Holdings, Inc. stockholder's (deficit) / equity	(23,647)	(51,351)
Noncontrolling interest
Total (deficit) / equity	(23,647)	(51,351)
Total liabilities and (deficit) / equity
Issuer [Member]
Current assets:
Cash	34,457	8,537	12,297	45,302
Accounts receivable, net of allowance	4,815	4,630
Inventories		343
Prepaid expenses and other current assets	10,030	9,229
Deferred income taxes	31,760	33,465
Income tax receivable, net	2,147	1,656
Total current assets	83,209	57,860
Property, plant and equipment, net	985	1,154
Investment in joint venture
Investment in subsidiaries	591,583	522,912
Intercompany accounts
Goodwill
Intangible assets, net
Deferred income taxes	6,826	6,138
Other noncurrent assets	15,878	17,115
Total assets	698,481	605,179
Current liabilities:
Accounts payable	290	1,398
Accrued liabilities	17,494	20,592
Accrued interest	3,395	3,287
Income taxes payable	39	248
Total current liabilities	21,218	25,525
Long-term debt	431,000	389,522
Other noncurrent liabilities	27,678	27,436
Obligations and advances in excess of investment in subsidiary
Intercompany accounts	235,087	205,218
Total liabilities	714,983	647,701
Commitments and contingencies
Global Brass and Copper Holdings, Inc. stockholder's (deficit) / equity	(16,502)	(42,522)
Noncontrolling interest
Total (deficit) / equity	(16,502)	(42,522)
Total liabilities and (deficit) / equity	698,481	605,179
Guarantor Subsidiaries [Member]
Current assets:
Cash
Accounts receivable, net of allowance	182,082	144,533
Inventories	181,937	158,713
Prepaid expenses and other current assets	14,925	2,600
Deferred income taxes
Income tax receivable, net
Total current assets	378,944	305,846
Property, plant and equipment, net	73,999	69,646
Investment in joint venture	2,168	2,972
Investment in subsidiaries	19,336	19,850
Intercompany accounts	253,943	223,081
Goodwill	4,399	4,399
Intangible assets, net	787	839
Deferred income taxes
Other noncurrent assets	916	640
Total assets	734,492	627,273
Current liabilities:
Accounts payable	108,410	77,390
Accrued liabilities	34,455	26,971
Accrued interest
Income taxes payable	44
Total current liabilities	142,909	104,361
Long-term debt
Other noncurrent liabilities
Obligations and advances in excess of investment in subsidiary
Intercompany accounts
Total liabilities	142,909	104,361
Commitments and contingencies
Global Brass and Copper Holdings, Inc. stockholder's (deficit) / equity	591,583	522,912
Noncontrolling interest
Total (deficit) / equity	591,583	522,912
Total liabilities and (deficit) / equity	734,492	627,273
Non-Guarantor Subsidiaries [Member]
Current assets:
Cash	4,207	5,446	3,424	4,648
Accounts receivable, net of allowance	16,443	15,154
Inventories	17,902	15,885
Prepaid expenses and other current assets	195	312
Deferred income taxes
Income tax receivable, net
Total current assets	38,747	36,797
Property, plant and equipment, net	346	327
Investment in joint venture
Investment in subsidiaries
Intercompany accounts
Goodwill
Intangible assets, net
Deferred income taxes
Other noncurrent assets
Total assets	39,093	37,124
Current liabilities:
Accounts payable	3,283	2,910
Accrued liabilities	736	861
Accrued interest
Income taxes payable	251	356
Total current liabilities	4,270	4,127
Long-term debt
Other noncurrent liabilities
Obligations and advances in excess of investment in subsidiary
Intercompany accounts	11,711	9,597
Total liabilities	15,981	13,724
Commitments and contingencies
Global Brass and Copper Holdings, Inc. stockholder's (deficit) / equity	19,336	19,850
Noncontrolling interest	3,776	3,550
Total (deficit) / equity	23,112	23,400
Total liabilities and (deficit) / equity	39,093	37,124
Eliminations [Member]
Current assets:
Cash	(4,654)	(121)	(3,559)	(413)
Accounts receivable, net of allowance
Inventories	(290)	(563)
Prepaid expenses and other current assets	(58)
Deferred income taxes
Income tax receivable, net		(356)
Total current assets	(5,002)	(1,040)
Property, plant and equipment, net
Investment in joint venture
Investment in subsidiaries	(610,919)	(542,762)
Intercompany accounts	(253,943)	(223,081)
Goodwill
Intangible assets, net
Deferred income taxes
Other noncurrent assets
Total assets	(869,864)	(766,883)
Current liabilities:
Accounts payable	(5,002)	(121)
Accrued liabilities
Accrued interest
Income taxes payable		(356)
Total current liabilities	(5,002)	(477)
Long-term debt
Other noncurrent liabilities
Obligations and advances in excess of investment in subsidiary	(16,502)	(42,522)
Intercompany accounts	(253,943)	(223,644)
Total liabilities	(275,447)	(266,643)
Commitments and contingencies
Global Brass and Copper Holdings, Inc. stockholder's (deficit) / equity	(594,417)	(500,240)
Noncontrolling interest
Total (deficit) / equity	(594,417)	(500,240)
Total liabilities and (deficit) / equity	$ (869,864)	$ (766,883)