Fair Value Measurements (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2014
Palmarejo Royalty Obligation [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the beginning of the period	$ 43,960	$ 40,338
Revaluation	(8,736)	6,560
Settlements	(4,963)	(16,637)
Balance at the end of the period	30,261	30,261
Rochester Royalty Obligation [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the beginning of the period	23,656	21,630
Revaluation	(4,345)	(1,835)
Settlements	(1,043)	(1,527)
Balance at the end of the period	$ 18,268	$ 18,268