Assets Acquired (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Significant Acquisitions and Disposals [Line Items]
Total assets acquired	$ 621,490	$ 293,555	$ 137,808
Total liabilities assumed		(14,592)
Net assets acquired	621,490	278,963	137,808
Land
Significant Acquisitions and Disposals [Line Items]
Total assets acquired	518	19,705	8,227
Buildings
Significant Acquisitions and Disposals [Line Items]
Total assets acquired	8,942	220,769	119,626
Intangible lease assets-subject to amortization
Significant Acquisitions and Disposals [Line Items]
Total assets acquired	1,040	20,630	9,955
Net Investment in Direct Financing Leases
Significant Acquisitions and Disposals [Line Items]
Total assets acquired	310,000
Mortgage Loans
Significant Acquisitions and Disposals [Line Items]
Total assets acquired	200,000
Other loans
Significant Acquisitions and Disposals [Line Items]
Total assets acquired	95,690	27,283
Equity Investments
Significant Acquisitions and Disposals [Line Items]
Total assets acquired	$ 5,300	$ 5,168