Income Tax Benefit (Provision) - Summary of Deferred Taxes (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Mar. 31, 2013
Deferred tax assets:
Reserves for expected costs of liquidation	$ 14,694
Net operating losses	226,419
Total deferred tax assets before valuation allowance	241,113
Less: Valuation allowance	(103,867)
Net deferred tax assets	137,246
Deferred tax liabilities:
Fair value in excess of tax basis of holdings of New GM Securities	(137,246)
Total deferred tax liability	(137,246)
Net deferred tax liability		$ (164,845)