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Commitments and contingencies (Details)
 1 Months Ended 12 Months Ended
Jan. 31, 2011
insurer
May 31, 2009
defendant
Dec. 31, 2016
USD ($)
defendant
case
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Dec. 31, 2012
USD ($)
Loss Contingencies [Line Items]              
Rent expense     $ 18,600,000 $ 20,900,000 $ 20,800,000    
Amount of letters of credit     $ 17,000,000        
Asbestos Litigation              
Loss Contingencies [Line Items]              
Number of defendants | defendant     1        
Portland Harbor Superfund Litigation              
Loss Contingencies [Line Items]              
Number of defendants | defendant   1          
Asbestos Litigation              
Loss Contingencies [Line Items]              
Annual out-of-pocket costs (less than)     $ 200,000 $ 200,000 $ 200,000 $ 200,000 $ 200,000
New claims filed each year (fewer than) | case     100        
Pending lawsuits (fewer than) | case     200        
Face amount of insurance coverage per occurrence (over)     $ 17,000,000        
Aggregate primary insurance coverage (over)     23,000,000        
Face amount of excess coverage (over)     $ 950,000,000        
Number of primary insurers under settlement agreement | insurer 7            
Percentage of costs of handling and settling each claim covered by insurance 80.00%