Note 2 - Securities (Details)		9 Months Ended
		Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Note 2 - Securities (Details) [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		$ 114,535,000	$ 264,699,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		2,343,000	3,576,000
Available-for-sale Debt Securities, Amortized Cost Basis		365,456,000
Available-for-sale Securities	[1]	$ 367,173,000	432,912,000
Debt Securities [Member]
Note 2 - Securities (Details) [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		161
State of Michigan and all its Political Subdivisions [Member]
Note 2 - Securities (Details) [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		$ 106,000,000	113,100,000
Available-for-sale Securities		106,900,000	113,900,000
All Other States and Their Political Subdivisions [Member]
Note 2 - Securities (Details) [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		25,900,000	30,000,000
Available-for-sale Securities		$ 26,000,000	30,000,000
Securities Other Than U.S. Government Agencies and the State of Michigan and Political Subdivisions [Member] | Stockholders' Equity, Total [Member] | Securities Issued Concentration Risk [Member]
Note 2 - Securities (Details) [Line Items]
Concentration Risk, Percentage		10.00%
U.S. Government Agency Debt Obligations and Mortgage-Backed Securities [Member]
Note 2 - Securities (Details) [Line Items]
Available-for-sale Securities, Restricted		$ 158,100,000	$ 167,600,000

[1] See Note 11 for a description of the fair value hierarchy as well as a disclosure of levels for classes of financial assets and liabilities.