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Investment in Other Affiliates Additional Information (Details) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Investments in and Advances to Affiliates [Line Items]          
Investments in and advances to affiliates $ 0   $ 0   $ 18,616,000
Income (loss) from equity method investments $ (111,000) $ (1,603,000) (25,576,000) $ (4,839,000)  
Cost-method Investments, Realized Gains     $ 13,000,000    
Eicher -Polaris Private Limited          
Investments in and Advances to Affiliates [Line Items]          
Equity method investment ownership percentage 50.00%   50.00%    
Period for proportionate share of income (loss) to be reflected in consolidated financials     1 month    
Equity Method Investment, Other than Temporary Impairment     $ 19,000,000    
Income (loss) from equity method investments $ 0   $ 23,447,000