Condensed Consolidated Statements of Changes in (Deficit)/Equity (USD $) In Thousands	Total	Common stock [Member]	Additional paid-in capital [Member]	(Accumulated deficit)/ Retained Earnings [Member]	Accumulated other comprehensive income [Member]	Receivables from stockholder [Member]	Total Global Brass and Copper Holdings, Inc. stockholder's equity [Member]	Noncontrolling interest [Member]
Stockholder's Equity, Beginning Balance at Dec. 31, 2011	$ 82,660	$ 211	$ 11,091	$ 68,718	$ 1,923	$ (2,451)	$ 79,492	$ 3,168
Profits interest compensation	19,517		19,517				19,517
Distribution to stockholder	(160,000)		(30,608)	(129,392)			(160,000)
Distribution to \ Payments from stockholder	(2,161)					(2,161)	(2,161)
Net (loss) income	(5,844)			(6,012)			(6,012)	168
Other comprehensive (loss) income, net of	(123)				(145)		(145)	22
Stockholder's Equity, Ending Balance at Jun. 30, 2012	(65,951)	211		(66,686)	1,778	(4,612)	(69,309)	3,358
Stockholder's Equity, Beginning Balance at Dec. 31, 2012	(47,801)	211		(48,153)	1,466	(4,875)	(51,351)	3,550
Profits interest compensation	29,271		29,271				29,271
Share-based compensation	181		181				181
Distribution to \ Payments from stockholder	4,875					4,875	4,875
Net (loss) income	(5,585)			(5,744)			(5,744)	159
Other comprehensive (loss) income, net of	(812)				(879)		(879)	67
Stockholder's Equity, Ending Balance at Jun. 30, 2013	$ (19,871)	$ 211	$ 29,452	$ (53,897)	$ 587		$ (23,647)	$ 3,776