Restructuring and Asset Impairment Charges (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restructuring Cost and Reserve [Line Items]
Workforce reductions at multiple sites			$ 1.3	$ 1.1	$ 0.0
Other restructuring charges			0.3	0.0	0.0
Total restructuring related charges			9.9	2.9	1.9
Asset impairment charges:
Goodwill impairment charges			1.6	0.0	11.2
Airplane impairment charges			2.3	0.3	0.0
Other impairment charges			0.5	0.0	0.0
Total asset impairment charges			4.4	0.3	11.2
Gain on sale of property and equipment, net:
Gain (Loss) on Disposition of Property Plant Equipment			(6.2)	0.3	(0.1)
Gain (Loss) on Disposition of Assets			(6.2)
Restructuring, impairment and other asset charges, net			8.1	3.2	13.1
Costs associated with exiting the wood pellet business | Facility Closing
Restructuring Cost and Reserve [Line Items]
Business exit costs			0.0	0.5	0.0
Costs associated with closing AMM | Facility Closing
Restructuring Cost and Reserve [Line Items]
Business exit costs			0.3	1.3	1.9
Costs associated with closing Albuquerque | Facility Closing
Restructuring Cost and Reserve [Line Items]
Business exit costs			1.3	0.0	0.0
Gain on sale of property and equipment, net:
Gain (Loss) on Disposition of Property Plant Equipment		$ (0.4)
Costs associated with closing Mequon | Facility Closing
Restructuring Cost and Reserve [Line Items]
Business exit costs			3.3	0.0	0.0
Gain on sale of property and equipment, net:
Gain (Loss) on Disposition of Property Plant Equipment	$ (4.7)
Costs associated with closing Enid | Facility Closing
Restructuring Cost and Reserve [Line Items]
Business exit costs			2.5	0.0	0.0
Costs associated with closing Tacoma | Facility Closing
Restructuring Cost and Reserve [Line Items]
Business exit costs			$ 0.9	$ 0.0	$ 0.0