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Note 3 - Securities (Details)	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Note 3 - Securities (Details) [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 163,876,000	$ 264,699,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	2,069,000	3,576,000
Proceeds from Sale of Available-for-sale Securities	1,483,000	0	$ 10,310,000
Available-for-sale Debt Securities, Amortized Cost Basis	344,796,000
Available-for-sale Securities	$ 346,992,000	432,912,000
Debt Securities [Member]
Note 3 - Securities (Details) [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	250
Mutual Funds [Member]
Note 3 - Securities (Details) [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	1
Municipal General Obligation Bonds [Member]
Note 3 - Securities (Details) [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 32,115,000	54,104,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	205,000	307,000
Proceeds from Sale of Available-for-sale Securities	1,500,000
Available-for-sale Securities	122,023,000	133,082,000
Michigan Strategic Fund Bonds [Member]
Note 3 - Securities (Details) [Line Items]
Available-for-sale Securities, Sold at Par			$ 10,300,000
State of Michigan and all its Political Subdivisions [Member]
Note 3 - Securities (Details) [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	106,000,000	113,000,000
Available-for-sale Securities	107,000,000	114,000,000
All Other States and Their Political Subdivisions [Member]
Note 3 - Securities (Details) [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	24,000,000	30,000,000
Available-for-sale Securities	$ 24,100,000	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 3 - Securities (Details) [Line Items]
Concentration Risk, Percentage	10.00%
U.S. Government Agency Debt Obligations and Mortgage-Backed Securities [Member]
Note 3 - Securities (Details) [Line Items]
Available-for-sale Securities, Restricted	$ 155,000,000	$ 168,000,000

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