Cash And Cash Equivalents And Investments (Schedule Of Investments) (Details) (USD $)	Jun. 30, 2012	Mar. 31, 2012
Short-term Investments, Total	$ 134,258,000	$ 111,137,000
Available-for-sale securities, long-term	13,600,000	25,900,000
Unrealized Loss	(1,700,000)	(2,150,000)
Amortized Cost	15,300,000	28,050,000
Certificates of Deposit [Member]
Available-for-sale securities	8,167,000	7,262,000
Unrealized Gain	3,000	4,000
Unrealized Loss	(13,000)	(9,000)
Amortized Cost	8,177,000	7,267,000
Equity Securities [Member]
Trading securities, short-term	8,616,000	8,650,000
US Government Agencies Debt Securities [Member]
Available-for-sale securities	29,657,000	26,010,000
Unrealized Gain	36,000	33,000
Unrealized Loss	(12,000)	(7,000)
Amortized Cost	29,633,000	25,984,000
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale securities	46,443,000	32,268,000
Unrealized Gain	60,000	39,000
Unrealized Loss	(55,000)	(21,000)
Amortized Cost	46,438,000	32,250,000
Corporate Debt Securities [Member]
Available-for-sale securities	41,375,000	36,947,000
Unrealized Gain	68,000	68,000
Unrealized Loss	(57,000)	(33,000)
Amortized Cost	41,364,000	36,912,000
Short-term Investments [Member]
Short-term Investments, Total	134,258,000	111,137,000
Unrealized Gain	167,000	144,000
Unrealized Loss	(137,000)	(70,000)
Total short-term investments, amortized cost	$ 134,228,000	$ 111,063,000