Fair Value Measurements (Details 2) - Jun. 30, 2015 - USD ($) $ in Thousands	Total	Total
Palmarejo Royalty Obligation [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the beginning of the period	$ 19,250	$ 21,912
Revaluation	(385)	1,159
Settlements	(3,584)	(7,790)
Balance at the end of the period	15,281	15,281
Rochester Royalty Obligation [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the beginning of the period	16,522	15,370
Revaluation	(1,137)	1,155
Settlements	(1,480)	(2,620)
Balance at the end of the period	13,905	13,905
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	1,379	1,379
Revaluation	(904)	(904)
Settlements	(386)	(386)
Balance at the end of the period	$ 89	$ 89