The current cash, cash equivalents and investments that are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against short-term borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. Includes current cash equivalents and investments that are similarly restricted as to withdrawal, usage or disposal.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 1

-Article 5

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.1)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

RESTRICTED INVESTMENTS AND BOND COLLATERAL - Additional Information (Detail) (USD $)	12 Months Ended			12 Months Ended
	Dec. 31, 2013	Mar. 31, 2014	Dec. 31, 2012	Dec. 31, 2013 Available-for-sale Securities [Member]	Dec. 31, 2012 Available-for-sale Securities [Member]	Dec. 31, 2011 Available-for-sale Securities [Member]	Dec. 31, 2013 Absaloka Mine	Dec. 31, 2013 Rosebud Mine
Schedule of Available-for-sale Securities [Line Items]
Gain on sale of available-for-sale securities held as restricted investments and bond collateral				$ 100,000	$ 100,000	$ 100,000
Reclamation Bond Collateral Released From Restriction							3,000,000	9,400,000
Number of months required funding in debt service reserve account	6 months
Letter of credit released from restriction	$ 5,998,000	$ 16,900,000	$ 0