Marketable Securities (Summary of available-for-sale securities ) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Mar. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Securities in a continuous loss position for less than 12 months	$ 1,125
Securities in a continuous loss position for more than 12 months	0
Aggregate fair value	1,125
Securities in a continuous loss position for less than 12 months	6
Securities in a continuous loss position for more than 12 months	0
Unrealized losses	6
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	21,385	23,183
Gross Unrealized Gains	2,320	2,249
Gross Unrealized Losses	6	39
Estimated fair value	$ 23,699	$ 25,393