Other, Net (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Income and Expenses [Abstract]
Foreign exchange gain (loss)	$ (11,456)	$ 1,281		$ (16,021)
Gain (loss) on sale of assets and investments	11,334	(1,037)		(352)
Gain on sale of the Joaquin project	0	21,138	$ 0	0
Gain on repurchase of the Rochester royalty obligation	0	2,332		0
Gain (loss) on the sale of the Endeavor stream and other royalties	0	1,036		0
Impairment of equity securities	(703)	(426)	(700)	(2,346)
Other	$ 923	2,319		1,052
Other, net		$ 26,643	$ 98	$ (17,667)