XML 59 R48.htm IDEA: XBRL DOCUMENT v3.7.0.1
Fair value measurements - Narrative (Details) - USD ($)
Jun. 30, 2017
Dec. 31, 2016
Financial Liabilities    
Assets fair value   $ 0
Significant transfers $ 0  
Restricted investment 70,400,000 $ 69,700,000
Reported Value    
Financial Liabilities    
Capital lease obligations 80,000,000  
Debt fair value 383,500,000  
Estimate of Fair Value    
Financial Liabilities    
Capital lease obligations 90,300,000  
Level 1 | Fair Value, Measurements, Recurring    
Financial Liabilities    
Restricted investment 70,400,000  
Restricted investments, fair value $ 68,100,000