Merger with Deltic (Narrative) (Details) $ in Thousands				3 Months Ended
		Feb. 20, 2018 USD ($) a Sawmill	Feb. 19, 2018 USD ($)	Mar. 31, 2018 USD ($)
Business Acquisition [Line Items]
Merger-related costs	[1]			$ 19,255
Deltic [Member]
Business Acquisition [Line Items]
Acres of timberland | a		530,000
Number of sawmills | Sawmill		2
Total assets acquired		$ 1,400,000
Equity consideration transferred		1,100,000
Liabilities assumed		$ 300,000
Merger-related costs				19,300
Restructuring costs, termination benefits				9,000
Merger related costs, professional fees				10,300
Revenue from acquired entity from date of acquisition				28,800
Loss before income taxes from acquired entity from date of acquisition				9,000
Non-recurring merger-related costs			$ 5,400	$ 24,700

[1] For integration and restructuring costs related to the merger with Deltic see Note 3: Merger with Deltic.