Income Tax (Details 1)	12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2010
Current:
Federal income tax statutory rate	35.00%	35.00%	35.00%
Increase (decrease) resulting from:
State income taxes, net of Federal benefit	4.50%	4.10%	4.30%
Research and development tax credits	(0.90%)	(1.00%)	(0.90%)
Qualified production activities income deduction	(3.00%)	(3.00%)	(2.00%)
Other	(0.60%)	(0.30%)	0.10%
Effective income tax rate	35.00%	34.80%	36.50%