Fair Value Measurements (Details 2) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2015
Palmarejo Royalty Obligation [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the beginning of the period	$ 15,281	$ 21,912
Revaluation	(2,983)	(1,823)
Settlements	(3,274)	(11,065)
Balance at the end of the period	9,024	9,024
Rochester Royalty Obligation [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the beginning of the period	13,905	15,370
Revaluation	(1,752)	(596)
Settlements	(1,213)	(3,834)
Balance at the end of the period	10,940	10,940
Available-for-sale Securities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the beginning of the period	89	1,379
Revaluation	0	(904)
Settlements	0	(386)
Balance at the end of the period	$ 89	$ 89