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Securities - Additional Information (Detail) (USD $) | 12 Months Ended
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Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items] |  |  |
Number of mutual funds with unrealized losses | 1 |  |
Fair value of debt securities with unrealized losses | $ 88,446,000 | $ 33,555,000 |
Aggregate depreciation of securities with unrealized losses | 10,100,000 | 388,000 |
Available for sale securities/Fair Value | 131,178,000 | 138,314,000 |
Total securities of specific issuer, other than U.S. Government and its agencies, maximum percentage of stockholders' equity | 10.00% |  |
Debt securities[Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Number of debt securities with unrealized losses | 65 |  |
Michigan Strategic Fund bonds [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Fair value of debt securities with unrealized losses | 0 | 0 |
Aggregate depreciation of securities with unrealized losses | 0 | 0 |
Securities available for sale | 10,300,000 | 0 | 0
Available for sale securities/Fair Value | 0 | 11,255,000 |
State of Michigan and all its political subdivisions [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Amortized cost of securities | 17,400,000 | 23,400,000 |
Available for sale securities/Fair Value | 17,800,000 | 24,600,000 |
U.S. Government agency debt obligations and mortgage-backed securities [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Carrying value of securities pledged to secure repurchase agreements | $ 94,400,000 | $ 83,800,000 |

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