Note 5 - Loans - Activity in the Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Balance at beginning of year				$ 118,966				$ 138,963	$ 118,966	$ 138,963	$ 161,420
Reversal for credit losses				(2,500)			$ (5,150)	(10,500)	(2,500)	(15,650)	(11,400)
Loans charged off									(4,173)	(18,903)	(20,427)
Recoveries of charged off loans									10,986	14,556	9,370
Balance at end of year	123,279				118,966				123,279	118,966	138,963
Provision/(reversal) for credit losses and transfers				(2,500)			$ (5,150)	(10,500)	(2,500)	(15,650)	(11,400)
Reserve for off Balance Sheet Credit Commitments [Member]
Balance at beginning of year				$ 3,224				$ 1,494	3,224	1,494	1,949
Reversal for credit losses									1,364	1,730	(455)
Balance at end of year	$ 4,588				$ 3,224				4,588	3,224	1,494
Provision/(reversal) for credit losses and transfers									$ 1,364	$ 1,730	$ (455)