Note 2 - Securities (Details)		3 Months Ended
		Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Note 2 - Securities (Details) [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		$ 88,370,000	$ 163,876,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		839,000	2,069,000
Available-for-sale Debt Securities, Amortized Cost Basis		339,690,000
Available-for-sale Securities	[1]	$ 343,805,000	346,992,000
Debt Securities [Member]
Note 2 - Securities (Details) [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		136
State of Michigan and all its Political Subdivisions [Member]
Note 2 - Securities (Details) [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		$ 112,000,000	106,000,000
Available-for-sale Securities		113,000,000	107,000,000
All Other States and Their Political Subdivisions [Member]
Note 2 - Securities (Details) [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		22,900,000	24,000,000
Available-for-sale Securities		23,200,000	24,100,000
U.S. Government Agency Debt Obligations and Mortgage-Backed Securities [Member]
Note 2 - Securities (Details) [Line Items]
Available-for-sale Securities, Restricted		$ 162,000,000	$ 155,000,000
Stockholders' Equity, Total [Member] | Securities Other Than U.S. Government Agencies and the State of Michigan and Political Subdivisions [Member] | Securities Issued Concentration Risk [Member]
Note 2 - Securities (Details) [Line Items]
Concentration Risk, Percentage		10.00%

[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.