Real Estate and Lending Activities - Schedule of Gross Assets by Operator (Detail) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Mar. 31, 2018	Dec. 31, 2017
Investment And Revenue From External Customers [Line Items]
Total Gross Assets		$ 9,031,840	$ 9,020,288
Total Gross Assets [Member] | Credit Concentration Risk [Member]
Investment And Revenue From External Customers [Line Items]
Total Gross Assets		$ 9,544,607	$ 9,476,212
Percentage of Total Gross Assets		100.00%	100.00%
Total Gross Assets [Member] | Credit Concentration Risk [Member] | Steward [Member]
Investment And Revenue From External Customers [Line Items]
Total Gross Assets	[1]	$ 3,459,275	$ 3,457,384
Percentage of Total Gross Assets	[1]	36.20%	36.50%
Total Gross Assets [Member] | Credit Concentration Risk [Member] | Prime [Member]
Investment And Revenue From External Customers [Line Items]
Total Gross Assets		$ 1,120,737	$ 1,119,484
Percentage of Total Gross Assets		11.70%	11.80%
Total Gross Assets [Member] | Credit Concentration Risk [Member] | MEDIAN [Member]
Investment And Revenue From External Customers [Line Items]
Total Gross Assets		$ 1,261,991	$ 1,229,325
Percentage of Total Gross Assets		13.20%	13.00%
Total Gross Assets [Member] | Credit Concentration Risk [Member] | Ernest [Member]
Investment And Revenue From External Customers [Line Items]
Total Gross Assets		$ 612,112	$ 629,161
Percentage of Total Gross Assets		6.40%	6.60%
Total Gross Assets [Member] | Credit Concentration Risk [Member] | RCCH [Member]
Investment And Revenue From External Customers [Line Items]
Total Gross Assets		$ 506,265	$ 506,265
Percentage of Total Gross Assets		5.30%	5.30%
Total Gross Assets [Member] | Credit Concentration Risk [Member] | Other Operators [Member]
Investment And Revenue From External Customers [Line Items]
Total Gross Assets		$ 2,118,132	$ 2,089,934
Percentage of Total Gross Assets		22.30%	22.10%
Total Gross Assets [Member] | Credit Concentration Risk [Member] | Other Assets Operators
Investment And Revenue From External Customers [Line Items]
Total Gross Assets		$ 466,095	$ 444,659
Percentage of Total Gross Assets		4.90%	4.70%

[1] Includes approximately $1.8 billion of triple net leased gross assets.