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Summary of Restructuring Related Obligations (Detail) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Firm Transportation Obligation [Roll Forward]      
Balance at beginning of period $ 14,790us-gaap_RestructuringReserve $ 15,993us-gaap_RestructuringReserve $ 15,993us-gaap_RestructuringReserve
Accretion 212pva_RestructuringReserveAccretionOfObligation 354pva_RestructuringReserveAccretionOfObligation 1,301pva_RestructuringReserveAccretionOfObligation
Cash payments, net (523)us-gaap_PaymentsForRestructuring   (2,504)us-gaap_PaymentsForRestructuring
Balance at end of period $ 14,479us-gaap_RestructuringReserve   $ 14,790us-gaap_RestructuringReserve