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
	Jun. 30, 2020	Jun. 30, 2019
Restructuring Cost and Reserve [Line Items]
Beginning Balance	$ 28,712	$ 37,485
Less reductions in reserves	(2,619)	(4,013)
Less liquidation costs incurred:
Ending Balance	21,261	31,037
Trust Professionals [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(1,689)	(1,262)
Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(1,052)	(1,079)
Other Administrative Expenses [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(2,091)	(94)
Reserve for Expected Wind-Down Costs [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	22,530	23,379
Less reductions in reserves	(2,612)	(2,855)
Less liquidation costs incurred:
Ending Balance	16,244	19,221
Reserve for Expected Wind-Down Costs [Member] | Trust Professionals [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(1,044)	(650)
Reserve for Expected Wind-Down Costs [Member] | Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(603)	(621)
Reserve for Expected Wind-Down Costs [Member] | Other Administrative Expenses [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(2,027)	(32)
Reserve for Expected Reporting Costs [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	6,100	13,996
Less reductions in reserves	(7)	(1,158)
Less liquidation costs incurred:
Ending Balance	4,934	11,714
Reserve for Expected Reporting Costs [Member] | Trust Professionals [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(645)	(612)
Reserve for Expected Reporting Costs [Member] | Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(450)	(450)
Reserve for Expected Reporting Costs [Member] | Other Administrative Expenses [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(64)	(62)
Reserve for Indenture Trustee/Fiscal and Paying Agent Costs [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	82	110
Less liquidation costs incurred:
Ending Balance	83	102
Reserve for Indenture Trustee/Fiscal and Paying Agent Costs [Member] | Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	$ 1	$ (8)