Note 8 - Employee Benefit Plans (Details) - Change in Benefit Obligation - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Change in benefit obligation:
Benefit obligation at beginning of year	$ 118,284	$ 118,284	$ 101,155
Service cost		4,216	4,312	$ 4,025
Interest cost		4,823	4,859	3,889
Actuarial (gain) loss		(2,617)	12,575
Fair value of plan assets at beginning of year	74,551	74,551	69,051
Actual (loss) return on plan assets		(2,221)	3,402
Employer contributions	$ 4,900	5,460	6,715
Benefits paid		(4,469)	(4,617)
Fair value of plan assets at end of year		73,321	74,551	69,051
Underfunded status at end of year		(46,916)	(43,733)
Benefit obligation at end of year		$ 120,237	$ 118,284	$ 101,155