Fair Value Measurements Fair Value Measurements (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 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	$ 40,338
Revaluation	4,019
Balance at the end of the period	44,357
Rochester Royalty Obligation [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the beginning of the period	21,630
Revaluation	673
Balance at the end of the period	$ 22,303