Note 8 - Employee Benefit Plans - Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Service cost	$ 4,309	$ 4,216	$ 4,312
Interest cost	5,229	4,823	4,859
Expected return on plan assets	(5,299)	(5,382)	(4,996)
Amortization of prior service benefit	(337)	(337)	(337)
Amortization of net gain from earlier periods	4,372	4,260	3,275
Net periodic pension cost	$ 8,274	$ 7,580	$ 7,113