Merger with Deltic - (Narrative) (Details) shares in Millions			3 Months Ended
		Feb. 20, 2018 a Sawmill	Mar. 31, 2018 USD ($) shares	Mar. 31, 2017 USD ($)
Business Acquisition [Line Items]
Number of share exchaged under agreement	[1]	180.00%
Consulting agreement period			2 years
Business combination recorded merger costs			$ 1,850,000
Merger-related costs	[2]		19,255,000
Deltic [Member]
Business Acquisition [Line Items]
Acres of timberland | a		530,000
Number of sawmills | Sawmill		2
Area of diversified timberland base after merger | a		2,000,000
Number of share exchaged under agreement		180.00%
Non-recurring merger-related costs			24,700,000	$ 0
Merger-related costs incurred prior to merger			$ 5,400,000
Stock dividend to be issued in connection with earnings and profits distribution. | shares			3.9
Earnings and profits dividend rate or special distribution percentage of stock		80.00%
Earnings and profits dividend rate or special distribution percentage of cash		20.00%
Deltic [Member] | Arkansas [Member]
Business Acquisition [Line Items]
Area of diversified timberland base after merger | a		930,000

[1] Exchange ratio per the merger agreement.

[2] For integration and restructuring costs related to the merger with Deltic see Note 14: Merger, Integration and Other Costs.