Holdings of New GM Securities at March 31, 2015 - Securities Pending Distribution or were Set Aside (Detail) $ in Thousands	Mar. 31, 2015 USD ($) shares
Summary of Investment Holdings [Line Items]
Fair Value	$ 372,237
New GM Common Stock [Member]
Summary of Investment Holdings [Line Items]
Number | shares	4,618,904
Fair Value	$ 173,209
New GM Series A Warrants [Member]
Summary of Investment Holdings [Line Items]
Number | shares	4,198,901
Fair Value	$ 116,520
New GM Series B Warrants [Member]
Summary of Investment Holdings [Line Items]
Number | shares	4,198,901
Fair Value	$ 82,508