Note 8 - Mergers and Acquisitions (Details)	Jan. 07, 2016 USD ($) $ / shares shares	Jan. 06, 2016	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Mar. 31, 2015 USD ($)
Note 8 - Mergers and Acquisitions (Details) [Line Items]
Assets			$ 883,517,000	$ 796,285,000	$ 867,985,000
Milton Bancorp, Inc. [Member]
Note 8 - Mergers and Acquisitions (Details) [Line Items]
Business Acquisition, Number of Issued and Outstanding Common Shares of Acquired Entity (in Shares) | shares	400
Business Combination, Number of Common Shares of the Acquiring Entity into Which CommonShares of the Acquired Entity May Be Converted (in Shares) | shares	1,636
Business Acquisition, Cash Which May Be Paid for the Stock of Acquired Entity	$ 37,219
Business Combination, Exchange of Acquired Entity's Common Shares for Cash or Common Shares of Acquiring Entity, Cash Reallocation Percentage	20.00%
Business Combination, Exchange of Acquired Entity's Common Shares for Cash or Common Shares of Acquiring Entity, Common Shares Reallocation Percentage	80.00%
Business Combination, Number of Acquired Entity's Preferred Shares to Be Converted into the Right to Receive Cash (in Shares) | shares	1,237
Business Combination, Conversion of Acquired Entity's Preferred Shares into the Right to Receive Cash, Cash Per Preferred Share (in Dollars per share) | $ / shares	$ 3,600
Number of Branches	19	5
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	$ 141,000,000
Business Combination, Loans Payable Assumed	110,000,000
Business Combination, Deposits Assumed	126,000,000
Business Combination, Consideration Transferred	20,000,000
Minimum [Member] | Milton Bancorp, Inc. [Member]
Note 8 - Mergers and Acquisitions (Details) [Line Items]
Assets	$ 900,000,000