Note 2 - Securities (Details Textual)	6 Months Ended
Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)
Debt Securities [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	93
State of Michigan and All Its Political Subdivisions [Member]
Available-for-sale Debt Securities, Amortized Cost Basis	$ 107,000,000	$ 106,000,000
Available-for-sale Securities	109,000,000	107,000,000
All Other States and Their Political Subdivisions [Member]
Available-for-sale Debt Securities, Amortized Cost Basis	21,500,000	24,000,000
Available-for-sale Securities	$ 21,800,000	24,100,000
Securities Other Than US Government Agencies and the State of Michigan and Political Subdivisions [Member] \| Stockholders' Equity, Total [Member] \| Securities Issued Concentration Risk [Member]
Concentration Risk, Percentage	10.00%
US Government Agency Debt Obligations and Mortgage Backed Securities [Member]
Available-for-sale Securities, Restricted	$ 137,000,000	155,000,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	30,509,000	163,876,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	182,000	2,069,000
Available-for-sale Debt Securities, Amortized Cost Basis	319,039,000
Available-for-sale Securities	$ 323,452,000	$ 346,992,000

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

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This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

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Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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