Quarterly report pursuant to Section 13 or 15(d)

Acquisitions (Details)

v3.10.0.1
Acquisitions (Details)
shares in Thousands, $ in Thousands, ¥ in Billions
3 Months Ended 6 Months Ended
Apr. 19, 2017
USD ($)
Rate
Apr. 19, 2017
JPY (¥)
Rate
Sep. 30, 2018
USD ($)
manufacturing_site
shares
Sep. 30, 2017
USD ($)
Rate
shares
Sep. 30, 2018
USD ($)
manufacturing_site
shares
Sep. 30, 2017
USD ($)
Rate
shares
Dec. 31, 2017
USD ($)
Rate
Dec. 31, 2017
JPY (¥)
Rate
Apr. 14, 2017
USD ($)
Apr. 14, 2017
JPY (¥)
Mar. 31, 2017
Rate
Business Acquisition [Line Items]                      
Foreign Currency Exchange Rate, Translation | Rate 10900.70% 10900.70%   11250.20%   11250.20% 11257.40% 11257.40%     11182.30%
Pro forma common shares - basic | shares     57,799 49,819 57,570 48,607          
Pro forma common shares - diluted | shares     59,197 58,409 59,119 58,136          
Equity income (loss) from equity method investments | $     $ 64 $ 224 $ (5) $ 75,641          
Acquisition (gain) loss | $     $ 0 $ (1,285) $ 0 $ (136,873)          
Business Acquisition Cost of Acquired Entity Working Capital Adjustment             $ 0 ¥ 0.3      
KEC [Member] | TOKIN [Member]                      
Business Acquisition [Line Items]                      
Equity Method Investment, Ownership Percentage 100.00% 100.00%                  
Business Acquisition, Percentage of Voting Interests Acquired 66.00% 66.00%                  
Payments to Acquire Businesses, Gross $ 148,600 ¥ 16.2                  
TOKIN [Member]                      
Business Acquisition [Line Items]                      
Number of Manufacturing Sites | manufacturing_site     6   6            
Disposal Group, Including Discontinued Operation, Consideration             $ 10,100 ¥ 1.1 $ 431,000 ¥ 48.2  
Stock Purchase Agreement [Member] | NEC TOKIN Corporation [Member] | KEMET Electronics Corporation [Member]                      
Business Acquisition [Line Items]                      
Equity Method Investment, Ownership Percentage     34.00%   34.00%            
Excess cash [Member] | KEC [Member] | TOKIN [Member]                      
Business Acquisition [Line Items]                      
Payments to Acquire Businesses, Gross 93,600 10.2                  
Cash Distribution [Member] | KEC [Member] | TOKIN [Member]                      
Business Acquisition [Line Items]                      
Payments to Acquire Businesses, Gross $ 55,000 ¥ 6.0