Stock Options and Stock-Based Compensation (Details 4) (USD $)	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Options outstanding
Options outstanding, beginning, Shares	751,023	813,662	1,065,403
Options outstanding, beginning, Weighted Average Exercise Per Share	$ 34.19	$ 29.26
Granted, Number of Options	123,100	149,075	207,325
Granted, Weighted Average Exercise Per Share	$ 46.08	$ 50.43	$ 42.40
Options exercised, Shares	(174,045)	(173,064)	(371,057)
Exercised, Weighted Average Exercise Per Share	$ 25.59	$ 25.00	$ 20.16
Cancelled - forfeited, Number of Options	(77,909)
Cancelled - forfeited, Weighted Average Exercise Per Share	$ 42.54
Cancelled- expired, Number of Options	(71,693)
Cancelled - expired, Weighted Average Exercise Per Share	$ 42.49
Options outstanding, ending, Shares	550,476	751,023	813,662
Options outstanding, ending, Weighted Average Exercise Per Share	$ 37.31	$ 34.19	$ 29.26
Options outstanding, Remaining Contractual Life (Years)	3 years 6 months 4 days
Options outstanding, Aggregate Intrinsic Value	$ 6,871,264
Options vested and expected to vest, Number of Options	488,743
Options vested and expected to vest, Weighted Average Exercise Per Share	$ 36.00
Options vested and expected to vest, Remaining Contractual Life (Years)	3 years 4 months 6 days
Options vested and expected to vest, Aggregate Intrinsic Value	6,722,829
Ending exercisable, Number of Options	278,962
Ending exercisable, Weighted Average Exercise Per Share	$ 29.51
Ending exercisable, Remaining Contractual Life (Years)	2 years 7 months 21 days
Ending exercisable, Aggregate Intrinsic Value	$ 5,585,463