Note 2 - Acquisitions and Divestitures - Net Cash (Received) Paid in Acquisitions and Divestitures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair value of assets and liabilities acquired:
Goodwill	$ 95,779	$ 95,779	$ 100,486	$ 100,722
Divestitures
Book value of assets sold		(165,742)	389
Book value of liabilities sold		111,198	(152)
Sales price in excess of net liabilities assumed		(3,682)	(6)
Total sales price		(58,226)	231
Cash sold
Amount due remaining on books		2,205	(231)
Net cash received in divestitures		(56,021)
Net cash (received) paid in acquisitions and divestitures		(29,716)	88
Acquisitions in 2016 [Member]
Fair value of assets and liabilities acquired:
Loans		149,122
Premises and equipment		4,829
Other assets		448
Other intangible assets		3,842
Deposits		(134,307)
Other liabilities		(75)
Goodwill		2,446
Total purchase price		26,305
Non-cash purchase price
Cash acquired
Net cash paid in acquisitions		$ 26,305
Acquisitions in 2015 [Member]
Fair value of assets and liabilities acquired:
Loans
Premises and equipment
Other assets
Other intangible assets
Deposits
Other liabilities
Goodwill			88
Total purchase price			88
Non-cash purchase price
Cash acquired
Net cash paid in acquisitions			$ 88