Reserves for Expected Costs of Liquidation and Residual Wind-Down Claims and Costs - Summary of Activity in Reserves for Expected Costs of Liquidation (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Restructuring Cost and Reserve [Line Items]
Beginning Balance	$ 21,261	$ 31,037	$ 28,712	$ 37,485
Less reductions in reserves	(3,716)		(6,335)
Plus net additions to reserves		31,517		27,504
Less liquidation costs incurred:
Ending Balance	6,650	59,759	6,650	59,759
Trust Professionals [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(476)	(1,686)	(2,165)	(2,948)
Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(1,006)	(1,070)	(2,058)	(2,149)
Other Administrative Expenses [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(9,413)	(39)	(11,504)	(133)
Reserve for Expected Wind-Down Costs [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	16,244	19,221	22,530	23,379
Less reductions in reserves	(2,054)		(4,666)
Plus net additions to reserves		23,578		20,723
Less liquidation costs incurred:
Ending Balance	4,312	41,065	4,312	41,065
Reserve for Expected Wind-Down Costs [Member] | Trust Professionals [Member]
Less liquidation costs incurred:
Liquidation costs incurred	68	(1,092)	(976)	(1,742)
Reserve for Expected Wind-Down Costs [Member] | Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(555)	(616)	(1,158)	(1,237)
Reserve for Expected Wind-Down Costs [Member] | Other Administrative Expenses [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(9,391)	(26)	(11,418)	(58)
Reserve for Expected Reporting Costs [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	4,934	11,714	6,100	13,996
Less reductions in reserves	(1,662)		(1,669)
Plus net additions to reserves		7,939		6,781
Less liquidation costs incurred:
Ending Balance	2,256	18,596	2,256	18,596
Reserve for Expected Reporting Costs [Member] | Trust Professionals [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(544)	(594)	(1,189)	(1,206)
Reserve for Expected Reporting Costs [Member] | Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(450)	(450)	(900)	(900)
Reserve for Expected Reporting Costs [Member] | Other Administrative Expenses [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(22)	(13)	(86)	(75)
Reserve for Indenture Trustee/Fiscal and Paying Agent Costs [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	83	102	82	110
Less liquidation costs incurred:
Ending Balance	82	98	$ 82	98
Reserve for Indenture Trustee/Fiscal and Paying Agent Costs [Member] | Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	$ (1)	$ (4)		$ (12)