Mineral Property - Capitalized Development Costs (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Property, Plant and Equipment [Abstract]
Development expenditures	$ 156	$ 485
Capitalized interest	169us-gaap_InterestPaidCapitalized	153us-gaap_InterestPaidCapitalized
Capitalized depreciation	2XPL_DepreciationCapitalized	8XPL_DepreciationCapitalized
Total capitalized costs	$ 327us-gaap_AcquisitionCosts	$ 646us-gaap_AcquisitionCosts

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=50486907&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