Geographic Information - Summary of Geographical Revenues and Assets (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Sep. 30, 2014
Sep. 30, 2013
Dec. 31, 2013
Revenues from External Customers and Long-Lived Assets [Line Items]          
Revenue $ 71,519 $ 57,257 $ 186,075 $ 159,806  
Property, Plant and Equipment, net 2,072,449   2,072,449   1,476,142
Geographical Information [Member]
         
Revenues from External Customers and Long-Lived Assets [Line Items]          
Revenue 71,519 57,257 186,075 159,806  
Property, Plant and Equipment, net 2,072,449   2,072,449   1,476,142
Geographical Information [Member] | United States [Member]
         
Revenues from External Customers and Long-Lived Assets [Line Items]          
Revenue 53,720 50,054 144,107 131,042  
Property, Plant and Equipment, net 1,489,030   1,489,030   1,210,319
Geographical Information [Member] | Canada [Member]
         
Revenues from External Customers and Long-Lived Assets [Line Items]          
Revenue 9,146 7,203 33,454 28,764  
Property, Plant and Equipment, net 245,996   245,996   265,823
Geographical Information [Member] | Chile [Member]
         
Revenues from External Customers and Long-Lived Assets [Line Items]          
Revenue 8,653    8,514     
Property, Plant and Equipment, net $ 337,423   $ 337,423