Activity Related to Restricted Stock-based Awards (Details) (USD $)	12 Months Ended
	Dec. 31, 2012
Restricted Stock
Number of Shares
Unvested at the beginning of the period (in shares)	48,924
Granted (in shares)	0
Forfeited (in shares)	(8,950)
Vested (in shares)	0
Unvested at the end of the period (in shares)	39,974
Weighted Average Grant-Date Price
Unvested shares at the beginning of the period (in dollars per share)	$ 40.20
Granted (in dollars per share)	$ 0.00
Forfeited (in dollars per share)	$ 48.87
Vested (in dollars per share)	$ 0.00
Unvested shares at the end of the period (in dollars per share)	$ 40.09
RSUs
Number of Shares
Unvested at the beginning of the period (in shares)	78,544
Granted (in shares)	239,618
Forfeited (in shares)	(92,848)
Vested (in shares)	(43,712)	[1]
Unvested at the end of the period (in shares)	181,602
Weighted Average Grant-Date Price
Unvested shares at the beginning of the period (in dollars per share)	$ 56.55
Granted (in dollars per share)	$ 23.12
Forfeited (in dollars per share)	$ 36.92
Vested (in dollars per share)	$ 17.38	[1]
Unvested shares at the end of the period (in dollars per share)	$ 32.15
PBRSUs
Number of Shares
Unvested at the beginning of the period (in shares)	0
Granted (in shares)	45,576
Forfeited (in shares)	(16,274)
Vested (in shares)	0
Unvested at the end of the period (in shares)	29,302
Weighted Average Grant-Date Price
Unvested shares at the beginning of the period (in dollars per share)	$ 0.00
Granted (in dollars per share)	$ 30.33
Forfeited (in dollars per share)	$ 30.33
Vested (in dollars per share)	$ 0.00
Unvested shares at the end of the period (in dollars per share)	$ 30.33

[1] a) deferral and conversion of a portion of fees payable to certain non-employee directors of the Company; b) deferral and conversion of a portion of the 2011 annual cash bonuses paid to certain executive officers and other employees of the Company; and c) RSUs with an accelerated vesting period that were granted to some employees of Molycorp Canada on the acquisition date.