v2.4.0.6
Fair value of financial instruments (Details 2) (USD $)
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Assets:      
Restricted cash $ 28,618,000 $ 21,412,000  
Liabilities:      
Increase in foreign exchange loss 547,000 13,838,000 (1,014,000)
Credit valuation adjustments
      
Liabilities:      
Net increase in fair value 18,400,000 5,800,000  
Pre-tax increase in other comprehensive income 1,100,000 900,000  
Increase in change in fair value of derivatives 13,800,000 5,100,000  
Credit valuation adjustments | Foreign currency forward contracts
      
Liabilities:      
Increase in foreign exchange loss (3,600,000) 200,000  
Recurring | Level 1
      
Assets:      
Cash and cash equivalents 60,191,000 60,651,000  
Restricted cash 28,618,000 21,412,000  
Total 88,809,000 82,063,000  
Recurring | Level 2
      
Assets:      
Derivative instruments asset 20,571,000 32,414,000  
Total 20,571,000 32,414,000  
Liabilities:      
Derivative instruments liability 151,108,000 53,762,000  
Total 151,108,000 53,762,000  
Recurring | Total
      
Assets:      
Cash and cash equivalents 60,191,000 60,651,000  
Restricted cash 28,618,000 21,412,000  
Derivative instruments asset 20,571,000 32,414,000  
Total 109,380,000 114,477,000  
Liabilities:      
Derivative instruments liability 151,108,000 53,762,000  
Total $ 151,108,000 $ 53,762,000