Annual report pursuant to Section 13 and 15(d)

Commitments and Contingencies - Additional Information (Details)

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Commitments and Contingencies - Additional Information (Details)
$ in Thousands
 1 Months Ended 6 Months Ended 12 Months Ended
Oct. 31, 2012
Mar. 31, 2015
Dec. 31, 2014
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Jun. 30, 2014
GBP (£)
Loss Contingencies [Line Items]              
Operating leases, rent expense       $ 6,362 $ 6,147 $ 6,070  
EEX              
Loss Contingencies [Line Items]              
Commitments as a result of acquisitions (up to)       $ 6,071     £ 4,500,000
Unfavorable Regulatory Action              
Loss Contingencies [Line Items]              
Anti-dumping duty rate 249.96%            
Countervailing duty rate, prior to increase 3.61%   3.61%        
Countervailing duty rate 15.24% 31.18%