Real Estate and Loans Receivable - Loans - Additional Information (Detail) $ in Thousands	Dec. 31, 2017 USD ($) Property Operator	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Business Acquisition [Line Items]
Existing mortgage loans	$ 1,778,264	$ 1,060,336	$ 757,500	$ 397,500
Ernest Transaction and Other Acquisitions [Member]
Business Acquisition [Line Items]
Existing mortgage loans	$ 114,000
Mortgage Loans [Member] | Steward [Member]
Business Acquisition [Line Items]
Number of Real Estate Properties | Property	14
Number Of Operators | Operator	4
Existing mortgage loans	$ 700,000