Note 9 - Goodwill and Core Deposit Intangible - Net (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2017	Oct. 01, 2015
Goodwill	$ 40,196,000	$ 40,196,000
Goodwill, Impaired, Accumulated Impairment Loss			$ 0
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	1,000,000
Finite-Lived Intangible Assets, Amortization Expense, Year Two	1,000,000
Finite-Lived Intangible Assets, Amortization Expense, Year Three	1,000,000
Finite-Lived Intangible Assets, Amortization Expense, Year Four	1,000,000
Finite-Lived Intangible Assets, Amortization Expense, Year Five	1,000,000
Finite-Lived Intangible Assets, Amortization Expense, after Year Five	$ 4,300,000
Minimum [Member]
Finite-Lived Intangible Asset, Useful Life	12 years
Maximum [Member]
Finite-Lived Intangible Asset, Useful Life	13 years
Core Deposits [Member] | Minimum [Member]
Finite-Lived Intangible Asset, Useful Life		12 years
Core Deposits [Member] | Maximum [Member]
Finite-Lived Intangible Asset, Useful Life		13 years
First National Security Company [Member]
Goodwill	$ 25,700,000
Acquisition of MNB [Member]
Goodwill	$ 14,500,000			$ 14,500,000