Fair value measurements (Recurring Fair Value Measurements) (Detail) - USD ($)
$ in Thousands
Mar. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Fair Value Hierarchy for Financial Instruments Measured at Fair Value on a Recurring Basis      
Derivative assets, gross $ 19,908    
Derivative assets, amount offset (363)    
Derivative liabilities, gross (363)    
Derivative liabilities, amounts offset 363    
Derivative assets, net 19,545    
Derivative assets (liabilities), net 19,545    
Predecessor      
Fair Value Hierarchy for Financial Instruments Measured at Fair Value on a Recurring Basis      
Derivative assets, gross   $ 184 $ 164,396
Derivative assets, amount offset   (184) (1,158)
Derivative liabilities, gross   (13,553) (1,158)
Derivative liabilities, amounts offset   184 1,158
Derivative assets, net   0 163,238
Derivative liabilities, net   (13,369) 0
Derivative assets (liabilities), net   (13,369) 163,238
Recurring Fair Value Measurements      
Fair Value Hierarchy for Financial Instruments Measured at Fair Value on a Recurring Basis      
Derivative assets, amount offset [1] (363)    
Derivative liabilities, amounts offset [1] 363    
Derivative assets amount offset (liabilities), net [1] 0    
Derivative assets, net 19,545    
Derivative liabilities, net 0    
Derivative assets (liabilities), net 19,545    
Recurring Fair Value Measurements | Significant Other Observable Inputs (Level 2)      
Fair Value Hierarchy for Financial Instruments Measured at Fair Value on a Recurring Basis      
Derivative assets, gross 19,432    
Derivative liabilities, gross (363)    
Derivative assets (liabilities), net 19,069    
Recurring Fair Value Measurements | Significant Unobservable Inputs (Level 3)      
Fair Value Hierarchy for Financial Instruments Measured at Fair Value on a Recurring Basis      
Derivative assets, gross 476    
Derivative liabilities, gross 0    
Derivative assets (liabilities), net $ 476    
Recurring Fair Value Measurements | Predecessor      
Fair Value Hierarchy for Financial Instruments Measured at Fair Value on a Recurring Basis      
Derivative assets, amount offset   (184) [1] (1,158) [2]
Derivative liabilities, amounts offset   184 [1] 1,158 [2]
Derivative assets amount offset (liabilities), net   0 [1] 0 [2]
Derivative assets, net   0 163,238
Derivative liabilities, net   (13,369) 0
Derivative assets (liabilities), net   (13,369) 163,238
Recurring Fair Value Measurements | Predecessor | Significant Other Observable Inputs (Level 2)      
Fair Value Hierarchy for Financial Instruments Measured at Fair Value on a Recurring Basis      
Derivative assets, gross   184 41,328
Derivative liabilities, gross   (13,455) (1,158)
Derivative assets (liabilities), net   (13,271) 40,170
Recurring Fair Value Measurements | Predecessor | Significant Unobservable Inputs (Level 3)      
Fair Value Hierarchy for Financial Instruments Measured at Fair Value on a Recurring Basis      
Derivative assets, gross   0 123,068
Derivative liabilities, gross   (98) 0
Derivative assets (liabilities), net   $ (98) $ 123,068
[1] Amounts represent the impact of master netting agreements that allow us to net settle positive and negative positions with the same counterparty. Positive and negative positions with a counterparty are netted only to the extent that they related to the same current versus noncurrent classification on the balance sheet.
[2] Amounts represent the impact of master netting agreements that allow us to net settle positive and negative positions with the same counterparty. Positive and negative positions with a counterparty are netted on the balance sheet only to the extent that they relate to the same current versus noncurrent classification.