Cash, Cash Equivalents And Marketable Securities (Narrative) (Details) (USD $)	3 Months Ended		12 Months Ended		3 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Mar. 31, 2010	Mar. 31, 2011	Jun. 30, 2011 Auction Rate Securities [Member]	Mar. 31, 2011 Auction Rate Securities [Member]	Jun. 30, 2011 Maximum [Member] months	Jun. 30, 2011 Minimum [Member] months
Long-term marketable securities maturity date, start date	July 2012		April 2012
Long-term marketable securities maturity date, end date	June 2038		June 2038
Short-term marketable securities maturity date, start date	July 2011		April 2011
Short-term marketable securities maturity date, end date	June 2012		March 2012
Long-term marketable securities	$ 27,442,000			$ 27,880,000	$ 17,200,000
Long-term marketable securities, face value					19,500,000
Long-term marketable securities, estimated market value					17,200,000
Auction rate securities, settled at par					4,250,000
Marketable securities	142,319,000			133,430,000		4,000,000
Proceeds from redeemed long-term marketable securities	32,253,000	17,404,000				250,000
Point basis of liquidity risk premium	350
Period used as basis for computation of weighted average assumption period for reclassification of security to liquidity							55	51
Cumulative temporary decline in value of marketable securities	2,300,000
Cumulative temporary decline in value of marketable securities net of tax	1,400,000
Valuation reserve	45,000
Valuation reserve, net of tax	$ 28,000