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Supplemental Oil and Gas Reserve Information - Unaudited - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2017 MBoe $ / bbl $ / MMBTU | Dec. 31, 2016 location MBoe $ / bbl $ / MMBTU | Dec. 31, 2015 MBoe $ / bbl $ / MMBTU
Reserve Quantities [Line Items] |  |  |
Net positive (negative) revisions of previous estimates (MMBoe) | (19,200) | 31,136 | (84,635)
Positive (negative) revisions of previous estimates - proved developed reserves (MMBoe) | (14,200) |  |
Positive (negative) revisions of previous estimates - proved undeveloped reserves (MMBoe) | (5,000) |  |
Proved undeveloped locations | location |  | 259 |
Proved undeveloped locations, net | location |  | 190.8 |
Additions due to extensions and discoveries (Energy) | 51,153 | 14,876 | 46,640
Estimated extensions and discoveries of reserves associated with new wells (Energy) | 17,900 | 6,200 | 20,400
Additional proved undeveloped reserves (Energy) | 33,300 | 6,500 | 26,300
Percentage of reserves produced from wells in certain formations | 100.00% | 100.00% | 100.00%
Percentage of proved undeveloped reserves |  | 100.00% | 100.00%
Divested reserves associated with non-operated properties (Energy) | 1,387 | 7,635 | 0
Purchases of reserves in place (Energy) | 671 | 66,936 | 2,565
Percentage of net positive (negative) revisions | (6.00%) | 14.00% | (31.00%)
Proved undeveloped reserves, decrease (Energy) |  | 71,500 |
Discount rate of future cash flows | 10.00% |  |
Unweighted arithmetic average first-day-of-the-month prices for oil, price per Bbl | $ / bbl | 51.34 | 42.60 | 50.16
Unweighted arithmetic average first-day-of-the-month prices for natural gas, price per MMBtu | $ / MMBTU | 2.99 | 2.47 | 2.63
Revision Due to Performance |  |  |
Reserve Quantities [Line Items] |  |  |
Net positive (negative) revisions of previous estimates (MMBoe) | (39,100) | 30,400 | 1,900
Positive (negative) revisions of previous estimates - proved developed reserves (MMBoe) | (29,700) |  |
Positive (negative) revisions of previous estimates - proved undeveloped reserves (MMBoe) | (9,400) |  |
Revision of Previous Estimate Due to (Mis)Alignment With Development Plan |  |  |
Reserve Quantities [Line Items] |  |  |
Net positive (negative) revisions of previous estimates (MMBoe) | (2,100) | (9,500) |
Positive (negative) revisions of previous estimates - proved undeveloped reserves (MMBoe) | (1,800) |  |
Revision of Previous Estimate Due to Realized Prices |  |  |
Reserve Quantities [Line Items] |  |  |
Net positive (negative) revisions of previous estimates (MMBoe) | 16,100 | (8,200) | (17,200)
Positive (negative) revisions of previous estimates - proved developed reserves (MMBoe) | 14,100 |  |
Positive (negative) revisions of previous estimates - proved undeveloped reserves (MMBoe) | 2,000 |  |
Revision of Previous Estimate Due to Ownership Adjustments |  |  |
Reserve Quantities [Line Items] |  |  |
Net positive (negative) revisions of previous estimates (MMBoe) | 2,500 | 8,200 | 3,000
Positive (negative) revisions of previous estimates - proved undeveloped reserves (MMBoe) | 2,600 |  |
Revision of Previous Estimate Due to Higher Gas to Oil Ratio |  |  |
Reserve Quantities [Line Items] |  |  |
Net positive (negative) revisions of previous estimates (MMBoe) |  | 8,200 |

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