Fair Value Measurements - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Mar. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured	$ 2,253,085,000		$ 2,253,085,000		$ 1,668,260,000
Liquidating distributions payable	100,447,000		100,447,000		16,555,000
Transfers between fair value amount	0	0	0	0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured	0		0		0
Liquidating distributions payable	$ 0		$ 0		$ 0