Dispositions - Revenue and Net Income (Loss) on Disposition (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue applicable to discontinued operations	$ 0	$ 0	$ 6,488
Net income (loss) from discontinued operations	(5,150)	(14,410)	86,245
Oman [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue applicable to discontinued operations	0	0	0
Net income (loss) from discontinued operations	(674)	(12,711)	(11,371)
Colombia [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue applicable to discontinued operations	0	0	0
Net income (loss) from discontinued operations	(4,476)	0	0
Antelope Project [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue applicable to discontinued operations	0	0	6,488
Net income (loss) from discontinued operations	$ 0	$ (1,699)	$ 97,616