Debt (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014	Sep. 30, 2016		Mar. 12, 2014
Long term debt and capital lease obligations
Current	$ 12,039	$ 10,431			$ 12,039
Debt	198,857	479,979			198,857
Interest expenses incurred for various debt instruments
Interest Paid on Senior Notes due 2021	28,871	33,437		$ 32,741
Interest Paid on Convertible Notes due 2028	13	54		173
Interest paid on term loan due 2020	4,939	4,719		0
Interest paid on short-term credit agreement	0	326		0
San Bartolomé Lines of Credit	15	795		0
Line of Credit Facility, Commitment Fee Amount	0	0		179
Write off revolver costs, interest expense	0	0		3,035
Interest Paid on Capital Leases	1,437	1,035		972
Accretion of Franco Nevada royalty obligation	1,211	6,567		10,773
Debt Issuance Cost	1,933	2,257		1,740
Amortization of debt issuance costs	(345)	(409)		(357)
Interest Expense, Debt	72	20		0
Capitalized interest	(1,226)	(3,098)		(1,710)
Total interest expense, net of capitalized interest	$ 36,920	45,703		$ 47,546
San Bartolome Letter of Credit Facility [Member]
Long term debt and capital lease obligations
Debt		4,571			0
3.25% Convertible Senior Notes due March 2028 [Member]
Long term debt and capital lease obligations
Debt		$ 712			$ 0
Debt Instrument, Interest Rate, Stated Percentage	3.25%	3.25%			3.25%
Senior Notes due 2021 [Member]
Long term debt and capital lease obligations
Debt Instrument, Face Amount							$ 150,000
Debt		$ 373,433	[1]		$ 175,991	[2]
Debt Instrument, Interest Rate, Stated Percentage	7.875%	7.875%
Capital Lease Obligations [Member]
Long term debt and capital lease obligations
Debt		$ 7,774			22,866
Senior Notes due 2021 [Member]
Long term debt and capital lease obligations
Current		0			0
3.25% Convertible Senior Notes due March 2028 [Member]
Long term debt and capital lease obligations
Current		0			0
Short Term Credit Agreement [Member]
Long term debt and capital lease obligations
Current		1,000			0
Debt		93,489			0
San Bartolome Letter of Credit Facility [Member]
Long term debt and capital lease obligations
Current		0			0
Capital Lease Obligations [Member]
Long term debt and capital lease obligations
Current		$ 9,431			$ 12,039

[1] (1)Net of unamortized debt issuance costs and premium received of $5.3 million.

[2] (1)Net of unamortized debt issuance costs and premium received of $2.0 million.