Real Estate and Loans Receivable - Capella Transaction - Additional Information (Detail) $ in Thousands		12 Months Ended
	Apr. 30, 2016 USD ($) Hospital	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
New loan for hospital property		$ 717,928	$ 612,836	$ 380,000
Capella [Member]
Business Acquisition [Line Items]
Net proceeds from transaction	$ 550,000
Net proceeds from equity investment and loans	492,000
Proceeds from prepayment of mortgage loans	210,000
New loan for hospital property	93,300
Investment on unsecured senior notes	50,000
Transaction costs incurred	$ 6,300
Number of hospital owned | Hospital	5
Write off of unbilled direct finance lease rent			$ 2,600
Capella [Member] | Master Lease [Member]
Business Acquisition [Line Items]
Term of lease, years	13 years 6 months
Capella [Member] | Other Stand-Alone Lease [Member]
Business Acquisition [Line Items]
Term of lease, years	11 years 6 months