Restructuring (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Asset impairments and restructuring
Restructuring charges (benefit)	$ 4,216	$ (2,463)	$ 6,662	$ 5,835
U.S. Operations
Asset impairments and restructuring
Restructuring charges (benefit)	3,200		4,500	700
Canadian and U.K. Operations
Asset impairments and restructuring
Restructuring charges (benefit)	800		1,600
Corporate Segment
Asset impairments and restructuring
Restructuring charges (benefit)	$ 200		$ 600	500
Wolverine, Brule and Willow Creek mines | Canadian and U.K. Operations
Asset impairments and restructuring
Restructuring charges (benefit)				$ 4,600