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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Restructuring Cost and Reserve [Line Items]
Beginning Balance	$ 19,145	$ 20,671	$ 18,903	$ 23,399
Plus additions to reserves	6,483	5,315	9,521	5,043
Less liquidation costs incurred:
Ending Balance	22,515	23,378	22,515	23,378
Liquidation Basis of Accounting [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance			18,903
Less liquidation costs incurred:
Ending Balance	22,515		22,515
Liquidation Basis of Accounting [Member] | Trust Professionals [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(2,015)	(1,335)	(3,580)	(2,469)
Liquidation Basis of Accounting [Member] | Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(1,061)	(1,233)	(2,235)	(2,456)
Liquidation Basis of Accounting [Member] | Other Administrative Expenses [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(37)	(40)	(94)	(139)
Reserve for Expected Wind-Down Costs [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	11,317	15,027	9,851	16,727
Plus additions to reserves	1,719	1,666	4,730	1,356
Less liquidation costs incurred:
Ending Balance	11,038	15,298	11,038	15,298
Reserve for Expected Wind-Down Costs [Member] | Liquidation Basis of Accounting [Member] | Trust Professionals [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(1,387)	(618)	(2,210)	(1,234)
Reserve for Expected Wind-Down Costs [Member] | Liquidation Basis of Accounting [Member] | Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(597)	(763)	(1,305)	(1,519)
Reserve for Expected Wind-Down Costs [Member] | Liquidation Basis of Accounting [Member] | Other Administrative Expenses [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(14)	(14)	(28)	(32)
Reserve for Expected Reporting Costs [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	7,619	5,368	8,827	6,379
Plus additions to reserves	4,764	3,649	4,791	3,687
Less liquidation costs incurred:
Ending Balance	11,282	7,824	11,282	7,824
Reserve for Expected Reporting Costs [Member] | Liquidation Basis of Accounting [Member] | Trust Professionals [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(628)	(717)	(1,370)	(1,235)
Reserve for Expected Reporting Costs [Member] | Liquidation Basis of Accounting [Member] | Trust Governance [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(450)	(450)	(900)	(900)
Reserve for Expected Reporting Costs [Member] | Liquidation Basis of Accounting [Member] | Other Administrative Expenses [Member]
Less liquidation costs incurred:
Liquidation costs incurred	(23)	(26)	(66)	(107)
Reserve for Indenture Trustee/Fiscal and Paying Agent Costs [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	209	276	225	293
Less liquidation costs incurred:
Ending Balance	195	256	195	256
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	$ (14)	$ (20)	$ (30)	$ (37)