Note 7 - Employee Benefit Plans - Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Service cost	$ 1,252	$ 1,196
Interest cost	1,377	1,339
Expected return on plan assets	(1,634)	(1,462)
Amortization of prior service benefit	15	(84)
Amortization of net loss	931	1,033
Net periodic benefit cost	$ 1,941	$ 2,022