Investments (Available for sale equity investments) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Mar. 31, 2021
Marketable Securities [Abstract]
Amortized cost, equity investments	$ 37,809	$ 29,809
Estimated market value, equity investments	54,904	42,117
Common stocks [Member]
Marketable Securities [Abstract]
Amortized cost, equity investments	9,775	9,775
Estimated market value, equity investments	24,728	20,440
Non-redeemable preferred stocks [Member]
Marketable Securities [Abstract]
Amortized cost, equity investments	28,034	20,034
Estimated market value, equity investments	$ 30,176	$ 21,677