Real Estate and Loans Receivable - Assets Acquired (Parenthetical) (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Loans repaid	[1]		$ 193,262	$ 385,851
Intangible Lease Assets - Subject to Amortization [Member]
Business Acquisition [Line Items]
Weighted average useful life of acquired intangible lease assets (in years)		28 years	28 years 6 months	30 years
Capella [Member]
Business Acquisition [Line Items]
Loans repaid			$ 93,300
Median [Member]
Business Acquisition [Line Items]
Loans repaid				$ 385,900
Prime [Member]
Business Acquisition [Line Items]
Loans repaid			$ 100,000

[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.