Fair Value Measurements - Narrative (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 31, 2017 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) milestone	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Jul. 31, 2017 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Write-Down of Manquiri Consideration		$ 0	$ 18,599	$ 0	$ 18,599
Senior Notes due 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net unamortized debt issuance costs		$ 3,300		$ 3,300		$ 4,100
Non-core three royalties and stream
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total consideration							$ 13,000
Convertible debenture							$ 6,700
JDS Silver Holdings Ltd.
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Purchase Commitment, Milestones | milestone				2
Silvertip Mine
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration payment	$ 25,000
Permitting payment, estimated discount rate (percentage)	2.50%
Resource declaration payment, estimated discount rate (percentage)	2.90%