Note 7 - Employee Benefit Plans - Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Service cost	$ 1,100	$ 1,252
Interest cost	1,620	1,377
Expected return on plan assets	(1,496)	(1,634)
Amortization of prior service cost	15	15
Amortization of net loss	1,097	931
Net periodic pension cost	$ 2,336	$ 1,941