Annual report pursuant to Section 13 and 15(d)

Acquisition Pro Forma (Details)

v3.10.0.1
Acquisition Pro Forma (Details) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 12 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Business Combinations [Abstract]                      
Revenues $ 404.3 $ 429.9 $ 459.4 $ 471.8 $ 424.9 $ 359.4 $ 374.8 $ 419.5 $ 1,765.4 $ 1,578.6 $ 1,338.3
Net sales:                      
Pro forma                   1,709.7 1,466.4
Net income attributable to Global Brass and Copper Holdings, Inc.:                      
As reported $ 6.6 $ 14.8 $ 21.0 $ 15.8 $ 5.6 $ 12.3 $ 15.7 $ 17.5 $ 58.2 51.1 32.2
Pro forma                   $ 55.5 $ 37.2
Net income attributable to Global Brass and Copper Holdings, Inc. per common share - Basic:                      
As reported (in usd per share) $ 0.30 $ 0.67 $ 0.95 $ 0.72 $ 0.26 $ 0.56 $ 0.72 $ 0.81 $ 2.66 $ 2.35 $ 1.50
Pro forma (in usd per share)                   2.55 1.74
Net income attributable to Global Brass and Copper Holdings, Inc. per common share - Diluted:                      
As reported (in usd per share) $ 0.29 $ 0.66 $ 0.94 $ 0.71 $ 0.25 $ 0.56 $ 0.71 $ 0.79 $ 2.61 2.31 1.49
Pro forma (in usd per share)                   $ 2.51 $ 1.72