Fair Value Measurements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain (loss) on derivative instruments	$ 0	$ (961)	$ (864)	$ (13,235)
Rochester Royalty Obligation [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain (loss) on derivative instruments	0	(851)	(864)	(5,787)
Palmarejo gold production royalty [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain (loss) on derivative instruments	0	(110)	0	(5,866)
Silver and gold options [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain (loss) on derivative instruments	$ 0	$ 0	$ 0	$ (1,582)