Condensed Consolidating Financial Information - Consolidating Statement of Comprehensive Income (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 income (loss)	$ (17,071)	$ (19,891)	$ (5,585)	$ (5,844)
Foreign currency translation adjustment, net of tax	(440)	(143)	(812)	(123)
Comprehensive income (loss)	(17,511)	(20,034)	(6,397)	(5,967)
Less: Comprehensive income attributable to noncontrolling interest	110	119	226	190
Comprehensive income (loss) attributable to Global Brass and Copper Holdings, Inc.	(17,621)	(20,153)	(6,623)	(6,157)
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(17,132)	(20,005)	(5,744)	(6,012)
Foreign currency translation adjustment, net of tax	(489)	(148)	(879)	(145)
Comprehensive income (loss)	(17,621)	(20,153)	(6,623)	(6,157)
Less: Comprehensive income attributable to noncontrolling interest
Comprehensive income (loss) attributable to Global Brass and Copper Holdings, Inc.	(17,621)	(20,153)	(6,623)	(6,157)
Issuer [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(14,178)	(19,734)	(2,553)	(5,560)
Foreign currency translation adjustment, net of tax	(489)	(148)	(879)	(145)
Comprehensive income (loss)	(14,667)	(19,882)	(3,432)	(5,705)
Less: Comprehensive income attributable to noncontrolling interest
Comprehensive income (loss) attributable to Global Brass and Copper Holdings, Inc.	(14,667)	(19,882)	(3,432)	(5,705)
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	15,422	13,946	36,487	35,356
Foreign currency translation adjustment, net of tax	(803)	(227)	(1,462)	(222)
Comprehensive income (loss)	14,619	13,719	35,025	35,134
Less: Comprehensive income attributable to noncontrolling interest
Comprehensive income (loss) attributable to Global Brass and Copper Holdings, Inc.	14,619	13,719	35,025	35,134
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	192	2,227	1,373	2,988
Foreign currency translation adjustment, net of tax	(177)	(520)	209	799
Comprehensive income (loss)	15	1,707	1,582	3,787
Less: Comprehensive income attributable to noncontrolling interest	110	119	226	190
Comprehensive income (loss) attributable to Global Brass and Copper Holdings, Inc.	(95)	1,588	1,356	3,597
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(1,375)	3,675	(35,148)	(32,616)
Foreign currency translation adjustment, net of tax	1,518	900	2,199	(410)
Comprehensive income (loss)	143	4,575	(32,949)	(33,026)
Less: Comprehensive income attributable to noncontrolling interest
Comprehensive income (loss) attributable to Global Brass and Copper Holdings, Inc.	$ 143	$ 4,575	$ (32,949)	$ (33,026)