Earnings Per Share - Basic and diluted earnings per share (Details) (USD $)	3 Months Ended	6 Months Ended
Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share [Abstract]
Numerator for earnings per share - net income	$ 4,329,701	$ 4,316,552	$ 9,238,889	$ 10,017,045
Denominator:
Denominator for basic earnings per share - weighted average shares	12,190,800	12,092,246	12,184,581	12,078,703
Effect of dilutive securities:
Stock options and other share awards	173,903	222,995	186,254	194,879
Denominator for diluted earnings per share	12,364,703	12,315,241	12,370,835	12,273,582
Earnings per share:
Basic (in dollars per share)	$ 0.36	$ 0.36	$ 0.76	$ 0.83
Diluted (in dollars per share)	$ 0.35	$ 0.35	$ 0.75	$ 0.82

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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