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	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Restructuring Cost and Reserve [Line Items]
Beginning Balance	$ 37,485	$ 38,087	$ 18,903
Plus net additions to (reductions in) reserves	1,522	9,511	33,948
Less liquidation costs incurred:
Ending Balance	28,712	37,485	38,087
Trust Professionals [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(5,633)	(5,238)	(10,093)
Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(4,293)	(4,530)	(4,404)
Other Administrative Expenses [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(369)	(345)	(267)
Reserve for Expected Wind-Down Costs [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	23,379	25,204	9,851
Plus net additions to (reductions in) reserves	5,059	4,122	25,351
Less liquidation costs incurred:
Ending Balance	22,530	23,379	25,204
Reserve for Expected Wind-Down Costs [Member] | Trust Professionals [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(3,330)	(3,125)	(7,424)
Reserve for Expected Wind-Down Costs [Member] | Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(2,465)	(2,695)	(2,523)
Reserve for Expected Wind-Down Costs [Member] | Other Administrative Expenses [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(113)	(127)	(51)
Reserve for Expected Reporting Costs [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	13,996	12,739	8,827
Plus net additions to (reductions in) reserves	(3,537)	5,389	8,597
Less liquidation costs incurred:
Ending Balance	6,100	13,996	12,739
Reserve for Expected Reporting Costs [Member] | Trust Professionals [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(2,303)	(2,113)	(2,669)
Reserve for Expected Reporting Costs [Member] | Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(1,800)	(1,801)	(1,800)
Reserve for Expected Reporting Costs [Member] | Other Administrative Expenses [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(256)	(218)	(216)
Reserve for Indenture Trustee/Fiscal and Paying Agent Costs [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	110	144	225
Less liquidation costs incurred:
Ending Balance	82	110	144
Reserve for Indenture Trustee/Fiscal and Paying Agent Costs [Member] | Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	$ (28)	$ (34)	$ (81)