Annual report pursuant to Section 13 and 15(d)

Supplemental Information on Oil and Gas Producing Activities - Changes in Standardized Measure of Discounted Future Net Cash Flows (Detail)

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Supplemental Information on Oil and Gas Producing Activities - Changes 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
Changes in Standardized Measure of Discounted Future Net Cash Flows:      
Balance at Beginning of Period $ 152,902 $ 166,187 $ 124,824
Sales of oil and gas, net of production costs (132,662) (168,563) (183,705)
Net changes in prices and production costs (52,056) (11,223) 194,633
Revisions of previous quantity estimates 43,815 155,111 75,713
Additions 29,620 69,092 7,742
Changes in estimated future development costs (5,345) (67,834) (5,831)
Development costs incurred during the period 44,389 34,944 31,913
Accretion of discount 15,290 16,619 12,482
Net change of income taxes 26,120 7,445 4,455
Change in production rates (timing) and other 15,363 (48,876) (96,039)
Balance at End of Period $ 137,436 $ 152,902 $ 166,187