Note 16 - Accumulated Other Comprehensive Income - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Balance	$ 862,825	$ 844,897	$ 764,339
Changes in fair value	469	32	254
Income tax expense	(183)	(13)	(99)
Balance	1,040,373	862,825	844,897
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Balance	(286)	(305)
Changes in fair value		32
Income tax expense	(183)	(13)
Reclassification of gain into income	469
Balance	$ 0	$ (286)	$ (305)