Fair Value Measurements (Details) (Fair value measurement, recurring basis [Member], USD $)	Apr. 30, 2013	Apr. 30, 2012
Financial assets and liabilities and redeemable noncontrolling interests on a recurring basis
Fair value adjustment to the borrowings subject to TRS	$ 10,044,000	$ 9,950,000
Redeemable noncontrolling interest	(238,942,000)	(239,136,000)
Fair value of financial assets and liabilities and redeemable noncontrolling interests on a recurring basis	(364,268,000)	(363,596,000)
Interest rate caps [Member]
Financial assets and liabilities and redeemable noncontrolling interests on a recurring basis
Derivative Assets	18,000	7,000
Interest rate swap agreements [Member]
Financial assets and liabilities and redeemable noncontrolling interests on a recurring basis
Derivative Assets		241,000
Derivative Liabilities	(128,552,000)	(129,522,000)
Total Return Swap [Member]
Financial assets and liabilities and redeemable noncontrolling interests on a recurring basis
Derivative Assets	20,305,000	21,066,000
Derivative Liabilities	(27,141,000)	(26,202,000)
Fair Value, Inputs, Level 1 [Member]
Financial assets and liabilities and redeemable noncontrolling interests on a recurring basis
Fair value adjustment to the borrowings subject to TRS	0	0
Redeemable noncontrolling interest	0	0
Fair value of financial assets and liabilities and redeemable noncontrolling interests on a recurring basis	0	0
Fair Value, Inputs, Level 1 [Member] | Interest rate caps [Member]
Financial assets and liabilities and redeemable noncontrolling interests on a recurring basis
Derivative Assets	0	0
Fair Value, Inputs, Level 1 [Member] | Interest rate swap agreements [Member]
Financial assets and liabilities and redeemable noncontrolling interests on a recurring basis
Derivative Assets		0
Derivative Liabilities	0	0
Fair Value, Inputs, Level 1 [Member] | Total Return Swap [Member]
Financial assets and liabilities and redeemable noncontrolling interests on a recurring basis
Derivative Assets	0	0
Derivative Liabilities	0	0
Fair Value, Inputs, Level 2 [Member]
Financial assets and liabilities and redeemable noncontrolling interests on a recurring basis
Fair value adjustment to the borrowings subject to TRS	0	0
Redeemable noncontrolling interest	0	0
Fair value of financial assets and liabilities and redeemable noncontrolling interests on a recurring basis	(2,363,000)	(2,768,000)
Fair Value, Inputs, Level 2 [Member] | Interest rate caps [Member]
Financial assets and liabilities and redeemable noncontrolling interests on a recurring basis
Derivative Assets	18,000	7,000
Fair Value, Inputs, Level 2 [Member] | Interest rate swap agreements [Member]
Financial assets and liabilities and redeemable noncontrolling interests on a recurring basis
Derivative Assets		241,000
Derivative Liabilities	(2,381,000)	(3,016,000)
Fair Value, Inputs, Level 2 [Member] | Total Return Swap [Member]
Financial assets and liabilities and redeemable noncontrolling interests on a recurring basis
Derivative Assets	0	0
Derivative Liabilities	0	0
Fair Value, Inputs, Level 3 [Member]
Financial assets and liabilities and redeemable noncontrolling interests on a recurring basis
Fair value adjustment to the borrowings subject to TRS	10,044,000	9,950,000
Redeemable noncontrolling interest	(238,942,000)	(239,136,000)
Fair value of financial assets and liabilities and redeemable noncontrolling interests on a recurring basis	(361,905,000)	(360,828,000)
Fair Value, Inputs, Level 3 [Member] | Interest rate caps [Member]
Financial assets and liabilities and redeemable noncontrolling interests on a recurring basis
Derivative Assets	0	0
Fair Value, Inputs, Level 3 [Member] | Interest rate swap agreements [Member]
Financial assets and liabilities and redeemable noncontrolling interests on a recurring basis
Derivative Assets		0
Derivative Liabilities	(126,171,000)	(126,506,000)
Fair Value, Inputs, Level 3 [Member] | Total Return Swap [Member]
Financial assets and liabilities and redeemable noncontrolling interests on a recurring basis
Derivative Assets	20,305,000	21,066,000
Derivative Liabilities	$ (27,141,000)	$ (26,202,000)