Subsequent Events (Detail) (Possible Loss of Funds [Member], Mauritania [Member], USD $)	Apr. 15, 2013	Jan. 31, 2013
Possible Loss of Funds [Member] \| Mauritania [Member]
Subsequent Event [Line Items]
Balance maintained in a foreign bank account that may be ceasing operations due to dispute	$ 2,900,000	$ 2,600,000

The amount of deposits held by branches of foreign institutions.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=7881181&loc=d3e65207-112826

Name:	us-gaap_ForeignFinancialInstitutionsActualDeposits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant