Related Party Transactions (Related Party Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Related party transactions:
Management fee revenue	$ 7,840	$ 7,233	$ 15,187	$ 14,389
Revenue from related parties	7,840	7,233	15,187	14,389
Blackwater [Member]
Related party transactions:
Management fee revenue	6,644	6,318	12,792	12,567
Mercury [Member]
Related party transactions:
Management fee revenue	$ 1,196	$ 915	$ 2,395	$ 1,822