Condensed Consolidating Financial Information - Consolidating Statement of Operations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Condensed Financial Statements, Captions [Line Items]
Net sales	$ 461,478	$ 416,979	$ 906,440	$ 860,370
Cost of sales	409,778	369,858	807,824	763,295
Gross profit	51,700	47,121	98,616	97,075
Selling, general and administrative expenses	52,855	37,965	72,533	55,888
Operating income (loss)	(1,155)	9,156	26,083	41,187
Interest expense	9,959	10,209	19,834	19,958
Loss on extinguishment of debt		19,612		19,612
Other (income) expense, net	4	398	191	709
Income (loss) before provision for (benefit from) income taxes and equity income (loss)	(11,118)	(21,063)	6,058	908
Provision for (benefit from) income taxes	6,461	(971)	12,503	7,227
Income (loss) before equity income (loss)	(17,579)	(20,092)	(6,445)	(6,319)
Equity income (loss), net of tax	508	201	860	475
Net income (loss)	(17,071)	(19,891)	(5,585)	(5,844)
Less: Net income attributable to noncontrolling interest	61	114	159	168
Net income (loss) attributable to Global Brass and Copper Holdings, Inc.	(17,132)	(20,005)	(5,744)	(6,012)
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Net sales
Cost of sales
Gross profit
Selling, general and administrative expenses	4,802	440	5,188	735
Operating income (loss)	(4,802)	(440)	(5,188)	(735)
Interest expense
Loss on extinguishment of debt
Other (income) expense, net
Income (loss) before provision for (benefit from) income taxes and equity income (loss)	(4,802)	(440)	(5,188)	(735)
Provision for (benefit from) income taxes	(1,848)	(169)	(1,997)	(283)
Income (loss) before equity income (loss)	(2,954)	(271)	(3,191)	(452)
Equity income (loss), net of tax	(14,178)	(19,734)	(2,553)	(5,560)
Net income (loss)	(17,132)	(20,005)	(5,744)	(6,012)
Less: Net income attributable to noncontrolling interest
Net income (loss) attributable to Global Brass and Copper Holdings, Inc.	(17,132)	(20,005)	(5,744)	(6,012)
Issuer [Member]
Condensed Financial Statements, Captions [Line Items]
Net sales
Cost of sales	(415)	654	116	(1,905)
Gross profit	415	(654)	(116)	1,905
Selling, general and administrative expenses	24,512	17,459	28,856	21,812
Operating income (loss)	(24,097)	(18,113)	(28,972)	(19,907)
Interest expense	9,959	10,209	19,834	19,961
Loss on extinguishment of debt		19,612		19,612
Other (income) expense, net	97	530	187	597
Income (loss) before provision for (benefit from) income taxes and equity income (loss)	(34,153)	(48,464)	(48,993)	(60,077)
Provision for (benefit from) income taxes	(4,553)	(14,784)	(9,953)	(19,161)
Income (loss) before equity income (loss)	(29,600)	(33,680)	(39,040)	(40,916)
Equity income (loss), net of tax	15,422	13,946	36,487	35,356
Net income (loss)	(14,178)	(19,734)	(2,553)	(5,560)
Less: Net income attributable to noncontrolling interest
Net income (loss) attributable to Global Brass and Copper Holdings, Inc.	(14,178)	(19,734)	(2,553)	(5,560)
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net sales	444,057	397,588	872,130	829,135
Cost of sales	394,201	352,200	777,054	738,120
Gross profit	49,856	45,388	95,076	91,015
Selling, general and administrative expenses	22,840	19,389	37,056	32,044
Operating income (loss)	27,016	25,999	58,020	58,971
Interest expense				(3)
Loss on extinguishment of debt
Other (income) expense, net	(213)	67	(83)	251
Income (loss) before provision for (benefit from) income taxes and equity income (loss)	27,229	25,932	58,103	58,723
Provision for (benefit from) income taxes	12,446	14,300	23,690	26,662
Income (loss) before equity income (loss)	14,783	11,632	34,413	32,061
Equity income (loss), net of tax	639	2,314	2,074	3,295
Net income (loss)	15,422	13,946	36,487	35,356
Less: Net income attributable to noncontrolling interest
Net income (loss) attributable to Global Brass and Copper Holdings, Inc.	15,422	13,946	36,487	35,356
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net sales	25,522	24,807	48,498	44,619
Cost of sales	24,093	22,420	44,842	40,464
Gross profit	1,429	2,387	3,656	4,155
Selling, general and administrative expenses	701	677	1,433	1,297
Operating income (loss)	728	1,710	2,223	2,858
Interest expense
Loss on extinguishment of debt
Other (income) expense, net	120	(199)	87	(139)
Income (loss) before provision for (benefit from) income taxes and equity income (loss)	608	1,909	2,136	2,997
Provision for (benefit from) income taxes	416	(318)	763	9
Income (loss) before equity income (loss)	192	2,227	1,373	2,988
Equity income (loss), net of tax
Net income (loss)	192	2,227	1,373	2,988
Less: Net income attributable to noncontrolling interest	61	114	159	168
Net income (loss) attributable to Global Brass and Copper Holdings, Inc.	131	2,113	1,214	2,820
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net sales	(8,101)	(5,416)	(14,188)	(13,384)
Cost of sales	(8,101)	(5,416)	(14,188)	(13,384)
Gross profit
Selling, general and administrative expenses
Operating income (loss)
Interest expense
Loss on extinguishment of debt
Other (income) expense, net
Income (loss) before provision for (benefit from) income taxes and equity income (loss)
Provision for (benefit from) income taxes
Income (loss) before equity income (loss)
Equity income (loss), net of tax	(1,375)	3,675	(35,148)	(32,616)
Net income (loss)	(1,375)	3,675	(35,148)	(32,616)
Less: Net income attributable to noncontrolling interest
Net income (loss) attributable to Global Brass and Copper Holdings, Inc.	$ (1,375)	$ 3,675	$ (35,148)	$ (32,616)