Mineral Properties - Capitalized Development Costs (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Abstract]
Development expenditures	$ 1,678	$ 1,854
Capitalized interest	633us-gaap_InterestPaidCapitalized	726us-gaap_InterestPaidCapitalized
Property payments	250us-gaap_AcquisitionCosts	174us-gaap_AcquisitionCosts
Capitalized depreciation	$ 21XPL_DepreciationCapitalized	$ 30XPL_DepreciationCapitalized

The capitalized costs incurred during the period (excluded from amortization) to purchase, lease or otherwise acquire an unproved property, including costs of lease bonuses and options to purchase or lease properties, the portion of costs applicable to minerals when land including mineral rights is purchased in fee, brokers' fees, recording fees, legal costs, and other costs incurred in acquiring properties.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-10.(c)(7)(ii))

-URI http://asc.fasb.org/extlink&oid=27015464&loc=d3e511914-122862

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 10

-Paragraph c

-Subparagraph 3(ii)(A)

-Article 4

Name:	us-gaap_AcquisitionCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration