Note 1 - Nature of Operations - Summary of Significant Accounting Policies - (Details Textual)		12 Months Ended
	Mar. 31, 2015 USD ($) $ / shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Number of Wealth Solution Offices		1
Held-to-maturity Securities		$ 0	$ 0
Trading Securities		0	0
Real Estate Acquired Through Foreclosure		227,000	1,187,000
Advertising Expense		762,000	849,000	$ 437,000
Core Deposits [Member]
Finite-Lived Intangible Asset, Useful Life				10 years
Residential Real Estate [Member]
Real Estate Acquired Through Foreclosure		$ 0	$ 0
American Gateway Financial Corporation [Member]
Number of Branches	10
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	$ 371,500,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables	143,200,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Marketable Securities	108,400,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deposits	$ 283,300,000
Business Acquisition, Cash Conversion Ratio Per Share | $ / shares	$ 10
Business Acquisition, Exchange Ratio	11.88
Business Combination, Consideration Transferred	$ 47,900,000