Note 8 - Employee Benefit Plans - Change in Benefit Obligation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Change in benefit obligation:
Benefit obligation at beginning of year	$ 120,237	$ 118,284
Service cost	4,309	4,216	$ 4,312
Interest cost	5,229	4,823	4,859
Actuarial loss (gain)	7,500	(2,617)
Benefits paid	(5,006)	(4,469)
Benefit obligation at end of year	132,270	120,237	118,284
Fair value of plan assets at beginning of year	73,321	74,551
Actual return (loss) on plan assets	9,950	(2,221)
Employer contributions	9,092	5,460
Benefits paid	(5,006)	(4,469)
Fair value of plan assets at end of year	87,357	73,321	$ 74,551
Underfunded status at end of year	$ (44,913)	$ (46,916)