Timber and Timberlands (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Timber And Timberlands [Abstract]
Depletion from Company Owned Lands	$ 17.0	$ 20.8	$ 25.3
Amortization of Logging Roads	$ 3.2	$ 3.1	$ 3.1