Stock-Based Compensation (Details) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 quarter	Jun. 30, 2012	Dec. 31, 2012
Stock-Based Compensation
Total cost of stock-based compensation	$ 128,567	$ 110,846	$ 260,675	$ 234,383
Amount of income tax benefit recognized in earnings	(21,799)	(13,507)	(43,803)	(45,923)
Amount charged against net income	106,768	97,339	216,872	188,460
Options
Assumptions used for estimating fair value of options using Black-Scholes option pricing model
Expected contractual term			7 years
Number of prior quarters used in calculation of dividend yield			4
Number of Shares
Outstanding at the beginning of the period (in shares)			838,662
Options granted (in shares)			10,000
Options cancelled/expired (in shares)			(11,150)
Options exercised (in shares)			(46,362)
Outstanding at the end of the period (in shares)	791,150		791,150		838,662
Exercisable at the end of the period (in shares)	613,775		613,775
Weighted Average Exercise Price per Share
Outstanding at the beginning of the period (in dollars per share)			$ 11.84
Options granted (in dollars per share)			$ 14.16
Options cancelled/expired (in dollars per share)			$ 14.34
Options exercised (in dollars per share)			$ 10.31
Outstanding at the end of the period (in dollars per share)	$ 11.87		$ 11.87		$ 11.84
Exercisable at the end of the period (in dollars per share)	$ 11.24		$ 11.24
Weighted Average Remaining Contractual Term
Outstanding at the end of the period (in years)			3 years 6 months		3 years 10 months 24 days
Options granted			6 months
Exercisable at the end of the period (in years)			2 years 9 months 18 days
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)	1,693,794		1,693,794		2,346,063
Options granted (in dollars)			0
Exercisable at the end of the period (in dollars)	1,640,000		1,640,000
Total intrinsic value of options exercised (in dollars)	$ 136,582	$ 16,607	$ 173,288	$ 292,377
2006 stock incentive plan
Stock-Based Compensation
Number of shares of common stock for options and other stock-based incentive awards that are still available for grant	272,552		272,552
2006 stock incentive plan and 1998 stock option plan
Stock-Based Compensation
Number of shares of common stock for options and other stock-based incentive awards that are still available for grant	791,150		791,150