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Note 3 - Securities (Details Textual)	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 253,210,000	$ 163,876,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	9,429,000	2,069,000
Proceeds from Sale of Available-for-sale Securities	264,000	1,483,000	$ 0
Available-for-sale Debt Securities, Amortized Cost Basis	336,562,000
Available-for-sale Securities	$ 328,060,000	346,992,000
Debt Securities [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	441
Mutual Funds [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	1
Municipal General Obligation Bonds [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 93,629,000	32,115,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	1,549,000	205,000
Proceeds from Sale of Available-for-sale Securities	300,000	1,500,000	$ 0
Available-for-sale Securities	119,047,000	122,023,000
State of Michigan and All Its Political Subdivisions [Member]
Available-for-sale Debt Securities, Amortized Cost Basis	109,000,000	106,000,000
Available-for-sale Securities	107,000,000	107,000,000
All Other States and Their Political Subdivisions [Member]
Available-for-sale Debt Securities, Amortized Cost Basis	19,500,000	24,000,000
Available-for-sale Securities	$ 19,500,000	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	$ 132,000,000	$ 155,000,000

X

- Definition

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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-SubTopic 10
-Section 50
-Paragraph 2
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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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The carrying amount of securities categorized neither as held-to-maturity nor trading which serve as security for borrowings or other arrangements.

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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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