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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Restructuring Cost and Reserve [Line Items]
Beginning Balance	$ 31,037	$ 30,340	$ 37,485	$ 38,087
Plus additions to reserves	31,517	13,053	27,504	8,579
Less liquidation costs incurred:
Ending Balance	59,759	41,897	59,759	41,897
Trust Professionals [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(1,686)	(368)	(2,948)	(2,239)
Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(1,070)	(1,081)	(2,149)	(2,388)
Other Administrative Expenses [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(39)	(47)	(133)	(142)
Reserve for Expected Wind-Down Costs [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	19,221	20,659	23,379	25,204
Plus additions to reserves	23,578	6,824	20,723	4,423
Less liquidation costs incurred:
Ending Balance	41,065	26,927	41,065	26,927
Reserve for Expected Wind-Down Costs [Member] | Trust Professionals [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(1,092)	90	(1,742)	(1,167)
Reserve for Expected Wind-Down Costs [Member] | Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(616)	(619)	(1,237)	(1,466)
Reserve for Expected Wind-Down Costs [Member] | Other Administrative Expenses [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(26)	(27)	(58)	(67)
Reserve for Expected Reporting Costs [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	11,714	9,547	13,996	12,739
Plus additions to reserves	7,939	6,229	6,781	4,156
Less liquidation costs incurred:
Ending Balance	18,596	14,847	18,596	14,847
Reserve for Expected Reporting Costs [Member] | Trust Professionals [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(594)	(458)	(1,206)	(1,072)
Reserve for Expected Reporting Costs [Member] | Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(450)	(451)	(900)	(901)
Reserve for Expected Reporting Costs [Member] | Other Administrative Expenses [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(13)	(20)	(75)	(75)
Reserve for Indenture Trustee/Fiscal and Paying Agent Costs [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	102	134	110	144
Less liquidation costs incurred:
Ending Balance	98	123	98	123
Reserve for Indenture Trustee/Fiscal and Paying Agent Costs [Member] | Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	$ (4)	$ (11)	$ (12)	$ (21)