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Goodwill and Intangibles - Additional Information (details) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Finite-Lived Intangible Assets [Line Items]      
Goodwill $ 384,387,000us-gaap_Goodwill $ 105,336,000us-gaap_Goodwill  
Amortization expense for intangible assets 4,300,000us-gaap_AmortizationOfIntangibleAssets 1,400,000us-gaap_AmortizationOfIntangibleAssets 1,100,000us-gaap_AmortizationOfIntangibleAssets
Estimated amortization expense for intangible assets in 2015 29,100,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths    
Estimated amortization expense for intangible assets in 2016 29,200,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo    
Estimated amortization expense for intangible assets in 2017 29,200,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree    
Estimated amortization expense for intangible assets in 2018 29,200,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour    
Estimated amortization expense for intangible assets in 2019 $ 29,200,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive    
Platte Valley [Member]      
Finite-Lived Intangible Assets [Line Items]      
Straight-line basis of amortization 50 years    
Chipeta Processing Limited Liability Company [Member]      
Finite-Lived Intangible Assets [Line Items]      
Straight-line basis of amortization 10 years    
Delaware Basin Midstream Limited Liability Company [Member]      
Finite-Lived Intangible Assets [Line Items]      
Straight-line basis of amortization 30 years