Note 7 - Income Taxes (Details Textual) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability	$ (146,000)
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			35.00%
Deferred Tax Assets, Valuation Allowance	75		$ 75	$ 1,532
Increase (Decrease) in Obligation, Pension Benefits			(7,400)	(600)	$ (5,800)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax			4,520	361	(3,528)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax			2,900	200	2,300
Income Taxes Paid, Net			2,000	14,600	$ 1,800
Accrued Income Taxes	13,800		13,800	14,600
Capital Loss Carryforward [Member]
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount			(1,400)	(200)
Domestic Tax Authority [Member]
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration				61,600
State and Local Jurisdiction [Member]
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration				101,700
State and Local Jurisdiction [Member] | Valuation Allowance, Operating Loss Carryforwards [Member]
Deferred Tax Assets, Valuation Allowance	$ 100		$ 100	$ 1,500
Scenario, Forecast [Member]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%