Schedule of Financial Instruments Having Difference Between Carrying Amount and Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Investment in direct financing lease, Carrying Amount	$ 9,642	$ 10,798
Note receivable from APM, Carrying Amount	4,896	4,749
Debt, Carrying Amount	(1,131,152)	(1,245,014)
Investment in direct financing lease, Fair Value	11,382	12,613
Note receivable from APM, Fair Value	8,827	7,825
Debt, Fair Value	$ (1,176,338)	$ (1,302,550)