Note 5 - Employee Benefit Plans - Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan [Abstract]
Service cost	$ 6,262	$ 5,820	$ 5,334
Interest cost	5,476	4,990	5,618
Expected return on plan assets	$ (13,452)	$ 9,252	$ (7,489)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Comprehensive Income (Loss), Net of Tax, Attributable to Parent	Comprehensive Income (Loss), Net of Tax, Attributable to Parent	Comprehensive Income (Loss), Net of Tax, Attributable to Parent
Amortization of prior service benefit	$ 511	$ 394	$ 117
Amortization of net gain from earlier periods	2,049	4,502	4,652
Net periodic pension cost	$ 846	$ 6,454	$ 8,232