v3.3.1.900
Summary of significant accounting policies - through derivatives (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2015
USD ($)
item
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Deferred financing costs      
Net carrying amount of deferred financing cost $ 42.5 $ 62.8  
Amortization expense 20.5 16.5 $ 8.0
Project development costs and capitalized interest      
Capitalized interest $ 0.0 $ 0.0 $ 1.9
Derivative financial instruments      
Number of interest rate swaps designated as cash flow hedges | item 1    
Minimum      
Deferred financing costs      
Amortization period 4 years    
Investments accounted for by the equity method      
Ownership level triggering equity method of accounting, as a percent 5.00%    
Maximum      
Deferred financing costs      
Amortization period 22 years    
Investments accounted for by the equity method      
Ownership level triggering equity method of accounting, as a percent 50.00%    
Impairment of long-lived assets, non-amortizing intangible assets and equity method investments      
Maximum percentage of ownership in entities in which consolidation is not required 50.00%