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Derivative Instruments - Narrative (Details)
3 Months Ended 12 Months Ended
Mar. 31, 2017
USD ($)
Bcf
MBbls
Dec. 31, 2016
USD ($)
MBbls
Dec. 31, 2015
Bcf
Derivative Instruments and Hedging Activities Disclosure [Abstract]      
Deferred net gains in accumulated other comprehensive income (loss), net of tax $ 8,700,000 $ 9,600,000  
Net gains on derivative commodity instruments $ 4,300,000    
Derivative Instruments, Gain (Loss) [Line Items]      
Maximum additional collateral as percentage of derivative liability 100.00%    
Aggregate fair value of derivative instruments with credit-risk related contingencies $ 91,200,000    
Collateral posted $ 0    
Propane swap      
Derivative Instruments, Gain (Loss) [Line Items]      
Volume of derivative instruments (in Bcf, Mbbls) | MBbls 1,008 1,095  
Cash flow hedging | Commodity derivatives      
Derivative Instruments, Gain (Loss) [Line Items]      
Volume of derivative instruments (in Bcf, Mbbls) | Bcf 805   703