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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Restructuring Cost and Reserve [Line Items]
Beginning Balance	$ 30,340	$ 19,145	$ 38,087	$ 18,903
Plus net additions to reserves	13,053	6,483	8,579	9,521
Less liquidation costs incurred:
Ending Balance	41,897	22,515	41,897	22,515
Liquidation Basis of Accounting [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance			38,087
Less liquidation costs incurred:
Ending Balance	41,897		41,897
Liquidation Basis of Accounting [Member] | Trust Professionals [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(368)	(2,015)	(2,239)	(3,580)
Liquidation Basis of Accounting [Member] | Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(1,081)	(1,061)	(2,388)	(2,235)
Liquidation Basis of Accounting [Member] | Other Administrative Expenses [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(47)	(37)	(142)	(94)
Reserve for Expected Wind-Down Costs [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	20,659	11,317	25,204	9,851
Plus net additions to reserves	6,824	1,719	4,423	4,730
Less liquidation costs incurred:
Ending Balance	26,927	11,038	26,927	11,038
Reserve for Expected Wind-Down Costs [Member] | Liquidation Basis of Accounting [Member] | Trust Professionals [Member]
Less liquidation costs incurred:
Liquidation costs incurred	90	(1,387)	(1,167)	(2,210)
Reserve for Expected Wind-Down Costs [Member] | Liquidation Basis of Accounting [Member] | Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(619)	(597)	(1,466)	(1,305)
Reserve for Expected Wind-Down Costs [Member] | Liquidation Basis of Accounting [Member] | Other Administrative Expenses [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(27)	(14)	(67)	(28)
Reserve for Expected Reporting Costs [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	9,547	7,619	12,739	8,827
Plus net additions to reserves	6,229	4,764	4,156	4,791
Less liquidation costs incurred:
Ending Balance	14,847	11,282	14,847	11,282
Reserve for Expected Reporting Costs [Member] | Liquidation Basis of Accounting [Member] | Trust Professionals [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(458)	(628)	(1,072)	(1,370)
Reserve for Expected Reporting Costs [Member] | Liquidation Basis of Accounting [Member] | Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(451)	(450)	(901)	(900)
Reserve for Expected Reporting Costs [Member] | Liquidation Basis of Accounting [Member] | Other Administrative Expenses [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(20)	(23)	(75)	(66)
Reserve for Indenture Trustee/Fiscal and Paying Agent Costs [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	134	209	144	225
Less liquidation costs incurred:
Ending Balance	123	195	123	195
Reserve for Indenture Trustee/Fiscal and Paying Agent Costs [Member] | Liquidation Basis of Accounting [Member] | Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	$ (11)	$ (14)	$ (21)	$ (30)