|
Principal Sources of Change in Standardized Measure of Discounted Future Net Cash Flows (Detail) (USD $)
In Thousands, unless otherwise specified
|
12 Months Ended |
|
Dec. 31, 2013
|
Dec. 31, 2012
|
Dec. 31, 2011
|
| Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items] |
|
|
|
| Standardized measure, beginning of year |
$ 872,000 |
$ 816,000 |
$ 587,000 |
| Sales of oil and gas produced, net of production costs |
(206,000) |
(157,000) |
(105,000) |
| Net changes in prices and production costs |
61,000 |
(201,000) |
274,000 |
| Purchases of minerals in place |
106,000 |
205,000 |
43,000 |
| Sales of minerals in place |
(84,000) |
(49,000) |
(5,000) |
| Previously estimated development costs incurred during the year |
89,000 |
102,000 |
64,000 |
| Extensions and discoveries |
111,000 |
105,000 |
25,000 |
| Changes in estimated future development costs |
(64,000) |
(102,000) |
(65,000) |
| Revisions of previous quantity estimates |
(203,000) |
39,000 |
11,000 |
| Accretion of discount |
79,000 |
77,000 |
60,000 |
| Net change in income taxes |
67,000 |
72,000 |
(53,000) |
| Changes in timing and other |
65,000 |
(35,000) |
(20,000) |
| Standardized measure, end of year |
$ 893,000 |
$ 872,000 |
$ 816,000 |