Merger with Deltic (Summary of Estimated Fair Value of Identifiable Assets Acquired and Liabilities Assumed) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018
ASSETS
Cash and cash equivalents	$ 3,419	$ 3,419
Customer receivables, net	12,709	12,709
Inventories	17,316	17,316
Other current assets	8,276	8,276
Real estate held for development and sale	77,000	79,000
Property, plant and equipment	261,331	265,901
Timber and timberlands	1,058,000	1,060,000
Mineral rights	6,236
Trade name and customer relationships intangibles	19,500	19,000
Other long-term assets	3,472	2,010
Total assets acquired	1,467,259	1,467,631
LIABILITIES
Accounts payable and accrued liabilities	12,754	12,604
Current portion of pension and other postretirement employee benefits	754	754
Long-term debt	229,968	229,968
Pension and other postretirement employee benefits	36,155	36,155
Deferred tax liabilities, net	43,917	44,439
Other long-term liabilities	936	936
Total liabilities assumed	324,484	324,856
Net assets acquired	1,142,775	$ 1,142,775
Measurement Period Adjustment [Member]
ASSETS
Real estate held for development and sale	(2,000)
Property, plant and equipment	(4,570)
Timber and timberlands	(2,000)
Mineral rights	6,236
Trade name and customer relationships intangibles	500
Other long-term assets	1,462
Total assets acquired	(372)
LIABILITIES
Accounts payable and accrued liabilities	150
Deferred tax liabilities, net	(522)
Total liabilities assumed	$ (372)