Holdings of New GM Securities - Pro Forma Adjustment Subsequent Loss on Liquidation of Securities (Detail) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Mar. 31, 2015	Mar. 31, 2014
Liquidation Basis of Accounting [Member]
Pro Forma Adjustment Subsequent Loss on Liquidation of Securities [Line Items]
Net Assets in Liquidation	$ 786,385	$ 1,130,736	$ 944,736	$ 1,064,494
Net Decrease in Net Assets in Liquidation	(158,351)	$ 66,242
Pro Forma Adjustment - Loss on Liquidation of New GM Securities in July 2015 [Member]
Pro Forma Adjustment Subsequent Loss on Liquidation of Securities [Line Items]
Net Assets in Liquidation	(48,221)
Net Decrease in Net Assets in Liquidation	(48,221)
Pro Forma as Adjusted [Member]
Pro Forma Adjustment Subsequent Loss on Liquidation of Securities [Line Items]
Net Assets in Liquidation	738,164
Net Decrease in Net Assets in Liquidation	$ (206,572)