Financial Instruments and Off-Balance Sheet Risk - Summary of Offsetting Arrangements (Detail) - USD ($)
$ in Thousands |
Dec. 31, 2016 |
Dec. 31, 2015 |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Gross Amounts of Recognized Assets |
$ 66,858
|
$ 157,714
|
| Gross Amounts Offset in the Balance Sheet, Assets |
0
|
0
|
| Amounts of Assets in Balance Sheet |
66,858
|
157,714
|
| Gross Amount Not Offset in the Balance Sheet, Financial Instruments |
(2,154)
|
(1,811)
|
| Cash Collateral Posted |
(209)
|
(1,798)
|
| Net Amount, Assets |
64,495
|
154,105
|
| Gross Amounts of Recognized Liabilities |
(95,339)
|
(37,178)
|
| Gross Amount Offset in the Balance Sheet, Liabilities |
0
|
0
|
| Amount of Liabilities in the Balance Sheet |
(95,339)
|
(37,178)
|
| Gross Amount Not Offset in the Balance Sheet, Financial Instruments |
2,154
|
1,811
|
| Cash Collateral Posted |
0
|
0
|
| Net Amount, Liabilities |
(93,185)
|
(35,367)
|
| Commodity derivatives |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Gross Amounts of Recognized Assets |
65,618
|
157,440
|
| Gross Amounts Offset in the Balance Sheet, Assets |
0
|
0
|
| Amounts of Assets in Balance Sheet |
65,618
|
157,440
|
| Gross Amount Not Offset in the Balance Sheet, Financial Instruments |
(2,154)
|
(1,811)
|
| Cash Collateral Posted |
(209)
|
(1,798)
|
| Net Amount, Assets |
63,255
|
153,831
|
| Gross Amounts of Recognized Liabilities |
(94,978)
|
(36,051)
|
| Gross Amount Offset in the Balance Sheet, Liabilities |
0
|
0
|
| Amount of Liabilities in the Balance Sheet |
(94,978)
|
(36,051)
|
| Gross Amount Not Offset in the Balance Sheet, Financial Instruments |
2,154
|
1,811
|
| Cash Collateral Posted |
0
|
0
|
| Net Amount, Liabilities |
(92,824)
|
(34,240)
|
| Interest rate swaps |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Gross Amounts of Recognized Assets |
1,240
|
274
|
| Gross Amounts Offset in the Balance Sheet, Assets |
0
|
0
|
| Amounts of Assets in Balance Sheet |
1,240
|
274
|
| Gross Amount Not Offset in the Balance Sheet, Financial Instruments |
0
|
0
|
| Cash Collateral Posted |
0
|
0
|
| Net Amount, Assets |
1,240
|
274
|
| Gross Amounts of Recognized Liabilities |
(336)
|
(1,115)
|
| Gross Amount Offset in the Balance Sheet, Liabilities |
0
|
0
|
| Amount of Liabilities in the Balance Sheet |
(336)
|
(1,115)
|
| Gross Amount Not Offset in the Balance Sheet, Financial Instruments |
0
|
0
|
| Cash Collateral Posted |
0
|
0
|
| Net Amount, Liabilities |
(336)
|
(1,115)
|
| Other |
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Gross Amounts of Recognized Liabilities |
(25)
|
(12)
|
| Gross Amount Offset in the Balance Sheet, Liabilities |
0
|
0
|
| Amount of Liabilities in the Balance Sheet |
(25)
|
(12)
|
| Gross Amount Not Offset in the Balance Sheet, Financial Instruments |
0
|
0
|
| Cash Collateral Posted |
0
|
0
|
| Net Amount, Liabilities |
$ (25)
|
$ (12)
|