Impairments (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure Text Block Supplement [Abstract]
Inventories, net									$ 4,100	$ 3,316
Property, plant and mine development, net									243,064	109,938
Operating lease right-of-use assets	$ 115,400								115,443	0
Goodwill									0	164,167
Intangible assets, net									1,240	4,478
Total	$ 363,717	$ 130	$ 0	$ 0	$ 265,715	$ 0	$ 16,184	$ 0	$ 363,847	$ 281,899	$ 0