Condensed Consolidated Statements of Cash Flows (Unaudited) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)		Sep. 30, 2018 USD ($)		Sep. 30, 2017 USD ($)
CASH FLOWS FROM OPERATING ACTIVITIES
Net income			$ 121,081		$ 74,865
Adjustments to reconcile net income to net cash from operating activities:
Depreciation, depletion and amortization	$ 19,445		53,685		21,908
Basis of real estate sold	4,248		10,673		6,351
Change in deferred taxes			13,879		(925)
Pension and other postretirement employee benefits			12,221		9,863
Equity-based compensation expense			6,518		3,536
Other, net			(1,220)		(1,467)
Change in working capital and operating-related activities, net			(13,289)		20,489
Real estate development expenditures			(3,081)
Funding of qualified pension plans			(52,099)		(5,275)
Net cash from operating activities			148,368		129,345
CASH FLOWS FROM INVESTING ACTIVITIES
Purchase of property, plant and equipment			(18,496)		(9,445)
Timberlands reforestation and roads			(12,464)		(11,577)
Acquisition of timber and timberlands			(166)		(22,033)
Other, net			655		(106)
Cash and cash equivalents acquired in Deltic merger			3,419
Net cash from investing activities			(27,052)		(43,161)
CASH FLOWS FROM FINANCING ACTIVITIES
Dividends to common stockholders			(75,305)		(45,686)
Proceeds from Potlatch revolving line of credit			100,000
Repayment of Potlatch revolving line of credit			(100,000)
Revolving line of credit repayment attributable to Deltic			(106,000)
Proceeds from issue of long-term debt			100,000
Repayment of long-term debt			(14,250)		(5,000)
Debt issuance costs			(2,434)
Other, net			(2,541)		(1,279)
Net cash from financing activities			(100,530)		(51,965)
Change in cash, cash equivalents and restricted cash			20,786		34,219
Cash, cash equivalents and restricted cash at beginning of period			120,457		82,584
Cash, cash equivalents and restricted cash at end of period	141,243		141,243		116,803
Cash paid during the period for:
Interest, net of amounts capitalized			23,183		17,381
Income taxes, net			10,335		13,923
NONCASH INVESTING AND FINANCING ACTIVITIES
Earnings and profits distribution payable			222,000
Cash and cash equivalents	137,535		137,535		$ 116,803
Restricted cash included in other long-term assets	$ 3,708	[1]	$ 3,708	[1]
Restricted Cash and Cash Equivalents, Noncurrent, Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent		us-gaap:OtherAssetsNoncurrent		us-gaap:OtherAssetsNoncurrent
Deltic [Member]
NONCASH INVESTING AND FINANCING ACTIVITIES
Equity issued as consideration for our merger with Deltic			$ 1,142,775

[1] Amounts included in restricted cash represent proceeds held by a qualified intermediary that are intended to be reinvested in timber and timberlands.