Fair Value (Details) (USD $)
Mar. 31, 2015
Dec. 31, 2014
Mar. 31, 2014
Fair Value      
Carrying value $ 1,580,687,000 $ 1,552,976,000  
Senior secured credit facility | Select      
Fair Value      
Carrying value 849,500,000 836,000,000  
Fair value 846,100,000 816,600,000  
6.375% senior notes      
Fair Value      
Carrying value 711,408,000 711,465,000  
Interest rate of debt (as a percent) 6.375% 6.375% 6.375%
6.375% senior notes | Select      
Fair Value      
Carrying value 711,400,000 711,500,000  
Fair value $ 701,100,000 $ 722,400,000  
Interest rate of debt (as a percent) 6.375% 6.375% 6.375%