Marketable Securities (Summary of available-for-sale securities ) (Details) $ in Thousands	12 Months Ended
	Mar. 31, 2018 USD ($)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 1,859
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1,285
Aggregate fair value	3,144
Equity securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,149
Gross Unrealized Gains	588
Gross Unrealized Losses	64
Estimated Fair Value	7,673
Securities in a continuous loss position for less than 12 months	26
Securities in a continuous loss position for more than 12 months	38
Unrealized losses	$ 64