Fair Value Measurements (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2014	Jun. 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	$ 44,357	$ 40,338
Revaluation	5,061	15,296
Settlements	(5,458)	(11,674)
Balance at the end of the period	43,960	43,960
Rochester Royalty Obligation [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the beginning of the period	22,303	21,630
Revaluation	1,837	2,510
Settlements	(484)	(484)
Balance at the end of the period	$ 23,656	$ 23,656