Note 7 - Employee Benefit Plans - Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Service cost	$ 1,196	$ 1,077	$ 3,588	$ 3,231
Interest cost	1,339	1,307	4,017	3,921
Expected return on plan assets	(1,462)	(1,325)	(4,386)	(3,975)
Amortization of prior service cost	(84)	(84)	(252)	(252)
Amortization of net (gain) loss	1,033	1,093	3,099	3,279
Net periodic pension cost	$ 2,022	$ 2,068	$ 6,066	$ 6,204