Note 5 - Loans - Activity in the Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Balance at beginning of year				$ 123,279				$ 118,966	$ 123,279	$ 118,966	$ 138,963
Reversal for credit losses		$ (1,500)		(3,000)				(2,500)	(4,500)	(2,500)	(15,650)
Loans charged off									(3,206)	(4,173)	(18,903)
Recoveries of charged off loans									6,818	10,986	14,556
Balance at end of year	122,391				123,279				122,391	123,279	118,966
(Reversal)/provision for credit losses and transfers		$ (1,500)		(3,000)				(2,500)	(4,500)	(2,500)	(15,650)
Reserve for off Balance Sheet Credit Commitments [Member]
Balance at beginning of year				$ 4,588				$ 3,224	4,588	3,224	1,494
Reversal for credit losses									(2,338)	1,364	1,730
Balance at end of year	$ 2,250				$ 4,588				2,250	4,588	3,224
(Reversal)/provision for credit losses and transfers									$ (2,338)	$ 1,364	$ 1,730