Stock-Based Compensation Plans (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	May. 28, 2015	May. 20, 2010	May. 24, 2007	Jun. 30, 2006
The 2007 plan
Stock-based compensation plans
Number of shares authorized	2,800,000	2,800,000				800,000		2,000,000
Options
Options cancelled (in shares)	135,368
Outstanding at the end of the period (in shares)	671,656	671,656
1996 Plan
Stock-based compensation plans
Number of shares authorized									3,025,000
Vesting period		10 years
Vesting rate (as a percent)		25.00%
Period of beginning of vesting of awards from grant date		1 year
Total intrinsic value of options exercised (in dollars)		$ 300,000	$ 200,000	$ 400,000
Options
Outstanding at the beginning of the period (in shares)		49,000	75,437	136,928
Options exercised (in shares)		(49,000)	(26,437)	(54,991)
Options cancelled (in shares)				(6,500)
Outstanding at the end of the period (in shares)	0	0	49,000	75,437	136,928
Options exercisable at the end of the period (in shares)			49,000	75,437
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)		$ 9.20	$ 9.38	$ 8.60
Options exercised (in dollars per share)		$ 9.20	9.71	7.96
Options cancelled (in dollars per share)				5.01
Outstanding at the end of the period (in dollars per share)			9.20	9.38	$ 8.60
Options exercisable at the end of the period (in dollars per share)			$ 9.20	$ 9.38
Weighted Average Remaining Contractual Term
Outstanding at the end of the period			7 months 2 days	1 year 5 months 27 days	2 years 2 months 23 days
Options exercisable at the end of the period			7 months 2 days	1 year 5 months 27 days
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)			$ 622,300	$ 601,991	$ 781,692
Options exercisable at the end of the period (in dollars)			$ 622,300	$ 601,991
Employee Stock Purchase Plan
Stock-based compensation plans
Number of shares authorized							250,000
Restricted stock | The 2007 plan
Stock-based compensation plans
Number of shares authorized	2,263,712	2,263,712