Securities - Additional Information (Detail) (USD $)	Sep. 30, 2013 Funds	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Number of mutual funds with unrealized losses	1
Fair value of debt securities with unrealized losses	$ 78,035,000	$ 33,555,000
Aggregate depreciation of securities with unrealized losses	(8,554,000)	(388,000)
Available for sale securities/Fair Value	123,793,000	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	59
State of Michigan and all its political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of securities	18,200,000	23,400,000
Available for sale securities/Fair Value	18,600,000	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	$ 85,200,000	$ 83,800,000