Note 4 - Loans - Activity in the Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Beginning Balance				$ 122,391				$ 123,279	$ 122,391	$ 123,279	$ 118,966
Reversal for credit losses	$ (5,000)	$ (2,000)	$ 0	0	$ 0	$ (1,500)	$ 0	(3,000)	(7,000)	(4,500)	(2,500)
Loans charged off									(6,997)	(3,206)	(4,173)
Recoveries of charged off loans									14,830	6,818	10,986
Ending Balance	123,224				122,391				123,224	122,391	123,279
Provision/(reversal) for credit losses and transfers	(5,000)	$ (2,000)	$ 0	0	0	$ (1,500)	$ 0	(3,000)	(7,000)	(4,500)	(2,500)
Reserve for off Balance Sheet Credit Commitments [Member]
Beginning Balance				$ 2,250				$ 4,588	2,250	4,588	3,224
Reversal for credit losses									1,605	(2,338)	1,364
Ending Balance	$ 3,855				$ 2,250				3,855	2,250	4,588
Provision/(reversal) for credit losses and transfers									$ 1,605	$ (2,338)	$ 1,364