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Other Financial Liabilities (debt) (Details Textual) - USD ($)
 1 Months Ended 3 Months Ended 12 Months Ended
Jun. 30, 2017
Jun. 27, 2016
Mar. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Mar. 31, 2014
Disclosure Of Other Financial Liabilities debt [Line Items]              
Notional amount   $ 275,000,000   $ 275,000,000 $ 275,000,000    
Borrowings       $ 272,575,000 271,881,000    
Borrowings, interest rate basis   Three-month Libor plus 3%          
Description of amortization of credit facility       The credit facility calls for amortization in four installments, with 15% of the total facility due on December 31, 2020 (US$5.0 million after the December 2017 repayment), 15% due on June 30, 2021 (US$225 million), 35% due on December 31, 2021 (US$525 million) and 35% due on June 19, 2022 (US$525 million).      
Repayments of borrowings, classified as financing activities       $ 300,000,000 $ 442,957,000 $ 90,000,000  
Write off debt issuance costs       4,300,000      
Issuance costs related to debt extinguishment       2,000,000      
Senior unsecured credit facility [Member]              
Disclosure Of Other Financial Liabilities debt [Line Items]              
Borrowings $ 1,500,000,000     1,300,000,000      
Repayments of borrowings, classified as financing activities     $ 525,000,000 $ 220,000,000      
Increased in Credit Facility $ 225,000,000            
Citi bank [Member] | Senior unsecured credit facility [Member]              
Disclosure Of Other Financial Liabilities debt [Line Items]              
Notional amount             $ 1,800,000,000
Citi bank [Member] | Term loan [Member]              
Disclosure Of Other Financial Liabilities debt [Line Items]              
Borrowings, interest rate basis       Interest on the credit facility is based on London Interbank Offered Rate (LIBOR) plus a spread (currently 1.9%) based on the Companys total net debt to earnings before interest, taxes, depreciation and amortization (EBITDA) ratio, as defined in the agreement.      
Sociedad Minera El Brocal S.A.A. [Member] | Citi bank [Member]              
Disclosure Of Other Financial Liabilities debt [Line Items]              
Borrowings, interest rate basis       Interest on the credit facility is based on London Interbank Offered Rate (LIBOR) plus a spread (currently 1.9%) based on the Company´s total net debt to earnings before interest, taxes, depreciation and amortization (EBITDA) ratio, as defined in the agreement.