Amortized Cost and Fair Value of Investment Securities (Detail) (USD $)
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Dec. 31, 2012
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Dec. 31, 2011
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Schedule of Available-for-sale Securities [Line Items] | ||
Amortized Cost | $ 413,973,929 | $ 363,539,526 |
Gross Unrealized gains | 8,240,983 | 8,447,266 |
Gross Unrealized Losses | 1,307,097 | 1,361,287 |
Fair Value | 420,907,815 | 370,625,505 |
Obligations of U.S. Government agencies
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Schedule of Available-for-sale Securities [Line Items] | ||
Amortized Cost | 269,193,449 | 234,356,518 |
Gross Unrealized gains | 546,153 | 722,520 |
Gross Unrealized Losses | 628,701 | 140,550 |
Fair Value | 269,110,901 | 234,938,488 |
Mortgage-backed Securities
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Schedule of Available-for-sale Securities [Line Items] | ||
Amortized Cost | 36,386,126 | 32,434,828 |
Gross Unrealized gains | 2,054,119 | 2,683,030 |
Gross Unrealized Losses | 18,944 | |
Fair Value | 38,421,301 | 35,117,858 |
State, county and municipal obligations
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Schedule of Available-for-sale Securities [Line Items] | ||
Amortized Cost | 105,300,892 | 93,654,718 |
Gross Unrealized gains | 5,640,711 | 5,041,716 |
Gross Unrealized Losses | 372,243 | 156,570 |
Fair Value | 110,569,360 | 98,539,864 |
Other investments
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Schedule of Available-for-sale Securities [Line Items] | ||
Amortized Cost | 3,093,462 | 3,093,462 |
Gross Unrealized Losses | 287,209 | 1,064,167 |
Fair Value | $ 2,806,253 | $ 2,029,295 |