Merger with Deltic (Summary of Total Consideration Transferred in Merger) (Details) $ / shares in Units, $ in Thousands	Feb. 20, 2018 USD ($) $ / shares shares
Business Acquisition [Line Items]
Exchange ratio	180.00%	[1]
Potlatch shares issued | shares	21,981,128
Price per Potlatch common share | $ / shares	$ 51.95	[2]
Aggregate value of Potlatch common shares issued | $	$ 1,141,920
Cash paid in lieu of fractional shares | $	14
Fair value of stock options and RSUs | $	841	[3]
Consideration transferred | $	$ 1,142,775
Deltic [Member]
Business Acquisition [Line Items]
Number of shares of Deltic common stock outstanding | shares	12,121,223	[4]
Number of Deltic performance awards | shares	90,515	[5]
Number of shares of common stock outstanding and performance awards | shares	12,211,738

[1] Exchange ratio per the merger agreement.

[2] Closing price of Potlatch common shares on February 20, 2018.

[3] Fair value of Deltic stock options for pre-combination services rendered that vested upon closing of the merger, as well as RSUs for pre-combination services rendered.

[4] Number of shares of Deltic common stock issued and outstanding as of February 20, 2018, net of fractional shares.

[5] Number of shares of Deltic performance awards for pre-combination services rendered that vested upon closing of the merger.