Investment in Oil and Gas Properties - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Capital expenditures related to oil and gas property investments	$ 576,395	$ 447,795
Canada
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Capital expenditures related to oil and gas property investments	$ 9,700

Capitalized costs of unproved properties incurred for any combination mineral interests acquisitions and other costs not previously disclosed within this table.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 13

-URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e61901-109447

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Properties

-URI http://asc.fasb.org/extlink&oid=21914647

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-Glossary Unproved Properties

-URI http://asc.fasb.org/extlink&oid=6527831

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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