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Note 3 - Securities (Details) | 12 Months Ended
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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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- 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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