Note 8 - Retirement Plans - Summary of Funded Status and Amounts Recognized on Balance Sheets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Projected benefit obligation at beginning of year	$ 103,199	$ 108,006
Service cost		3,130	$ 5,162
Interest cost	4,398	4,159	4,106
Actuarial losses	1,839	420
Benefits paid	(2,790)	(1,683)
Effect of pension curtailment		(10,833)
Merger of the Assumed Plans	8,330
Projected benefit obligation at end of year	114,976	103,199	108,006
Fair value of pension plan assets at beginning of year	69,246	66,813
Actual return on plan assets	5,918	(1,034)
Company contributions	2,775	5,150
Merger of the Assumed Plans	5,780
Fair value of pension plan assets at end of year	80,929	69,246	$ 66,813
Funded status of pension plan	(34,047)	(33,953)
Accrued benefit cost	(5,121)	(8,994)
Accumulated other comprehensive loss	(28,926)	(24,959)
Net liability recognized	$ (34,047)	$ (33,953)