Summary of Significant Accounting Policies - Unproved Property Costs (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Unproved property cost	$ 103,917	$ 78,453
Budong PSC [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Unproved property cost	4,470	5,219
Dussafu PSC [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Unproved property cost	$ 99,447	$ 73,234