Real Estate and Loans Receivable - Assets Acquired (Detail) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Equity investments and other assets		$ 100,000	$ 70,166	$ 101,716
Liabilities assumed		(878)	(6,319)	(317)
Total assets acquired		2,246,788	1,682,409	2,218,869
Loans repaid	[1]		(193,262)	(385,851)
Total net assets acquired		2,246,788	1,489,147	1,833,018
Land [Member]
Business Acquisition [Line Items]
Total assets acquired		229,091	91,071	120,746
Building [Member]
Business Acquisition [Line Items]
Total assets acquired		1,027,154	655,324	741,935
Intangible Lease Assets - Subject to Amortization [Member]
Business Acquisition [Line Items]
Total assets acquired		150,971	94,167	176,383
Net Investments in Direct Financing Leases [Member]
Business Acquisition [Line Items]
Total assets acquired		40,450	178,000	174,801
Other Loans [Member]
Business Acquisition [Line Items]
Total assets acquired				523,605
Mortgage Loans [Member]
Business Acquisition [Line Items]
Total assets acquired		$ 700,000	$ 600,000	$ 380,000

[1] The 2016 column includes $93.3 million of loans advanced to Capella in 2015 and repaid in 2016 as a part of the Capella transaction, along with $100.0 million loans advanced to Prime in 2015 and repaid in 2016 as part of the sale leaseback conversion of four properties in New Jersey. The 2015 column includes $385.9 million of loans advanced to MEDIAN in 2014 and repaid in 2015 as a part of the MEDIAN transaction.