XML 51 R39.htm IDEA: XBRL DOCUMENT v3.5.0.2
Business acquisitions - Acquisition of Mt. Holly smelter narrative (Details) - USD ($)
$ in Thousands
 1 Months Ended 3 Months Ended 9 Months Ended
Dec. 01, 2014
Mar. 31, 2016
Apr. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Business Acquisition [Line Items]              
Gains recognized on contingent consideration       $ 0 $ 1,523 $ 0 $ 18,337
Total net consideration paid $ 41,487            
Mt. Holly Smelter [Member]              
Business Acquisition [Line Items]              
Purchase price 67,500            
Non-cash pre-tax gain at closing 15,955            
Acquisition costs 1,539            
Consideration received for expected future post-employment benefits $ 2,400            
Consideration received for working capital adjustments     $ 11,313        
Proceeds from acquisition - contingent consideration   $ 12,500          
Gains recognized on contingent consideration         $ 1,523   $ 18,337