Condensed Consolidated Statements of Income (Unaudited) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Revenues		$ 268,233	$ 163,229	$ 468,130	$ 312,910
Costs and expenses:
Cost of goods sold		180,906	111,356	320,061	223,854
Selling, general and administrative expenses		16,892	13,079	30,548	24,447
Deltic merger-related costs	[1]	1,018		20,273
Gain on lumber price swap			(3,265)		(3,265)
Total costs and expenses		198,816	121,170	370,882	245,036
Operating income		69,417	42,059	97,248	67,874
Interest expense, net		(9,356)	(7,348)	(15,016)	(12,318)
Non-operating pension and other postretirement employee benefit costs		(1,908)	(1,286)	(3,765)	(3,192)
Income before income taxes		58,153	33,425	78,467	52,364
Income taxes		(12,005)	(9,181)	(17,722)	(11,199)
Net income		$ 46,148	$ 24,244	$ 60,745	$ 41,165
Net income per share:
Basic (in dollars per share)		$ 0.73	$ 0.59	$ 1.07	$ 1.01
Diluted (in dollars per share)		0.73	0.59	1.06	1.00
Dividends per share (in dollars per share)		$ 0.40	$ 0.375	$ 0.80	$ 0.75
Weighted-average shares outstanding (in thousands):
Basic (in shares)		62,979,660	40,822,726	56,739,012	40,802,057
Diluted (in shares)		63,316,291	41,218,969	57,128,020	41,143,695

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