Fair Value Measurements (Tables)

12 Months Ended

Mar. 31, 2013

Fair Value Measurements [Abstract]

Assets and liabilities measured at fair value on a recurring basis

	March 31, 2013
(in thousands)	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents:
Money market funds	$	354	$	—	$	—	$	354
Marketable Securities:
Municipal commercial paper and demand notes		—		61,006		—		61,006
Corporate commercial paper		—		15,790		—		15,790
Holdings of New GM Securities
New GM Common Stock		798,848		—		—		798,848
New GM Warrants		792,262		—		—		792,262
Total Assets	$	1,591,464	$	76,796	$	—	$	1,668,260
Liabilities:
Liquidating distributions payable	$	16,555	$	—	$	—	$	16,555

	March 31, 2012
(in thousands)	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents:
Money market funds	$	38,396	$	—	$	—	$	38,396
Marketable Securities:
Municipal commercial paper and demand notes		—		25,253		—		25,253
Corporate commercial paper		—		59,317		—		59,317
U.S. government agency bonds		—		2,001		—		2,001
Holdings of New GM Securities
New GM Common Stock		770,389		—		—		770,389
New GM Warrants		759,873		—		—		759,873
Total Assets	$	1,568,658	$	86,571	$	—	$	1,655,229
Liabilities:
Liquidating distributions payable	$	31,720	$	—	$	—	$	31,720