Summary of Significant Accounting Policies - Narrative (Details) ft² in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) ft² land_parcel reporting_unit state property	Dec. 31, 2017 USD ($) land_parcel property	Dec. 31, 2016 USD ($) property
Business Overview [Abstract]
Gross investment, amount, total	$ 4,000,000,000.0
Real estate properties and mortgages | property	199
Number of owned real estate properties | property	199
Number of states that the Company owns real estate in | state	27
Square footage of owned real estate properties | ft²	14.8
Approximate square feet for which Nationwide property management services provided by company | ft²	11.2
Segment Reporting [Abstract]
Number of Reporting Units | reporting_unit	1
Real Estate Properties [Abstract]
Total real estate properties	$ 3,974,071,000	$ 3,838,638,000
Elimination of real estate lease intangibles against accumulated depreciation	23,200,000	16,600,000
Depreciation	$ 143,800,000	$ 129,400,000	$ 116,500,000
Maximum period up to which interest capitalize on properties in stabilization	1 year
Land Held for Development [Abstract]
Number of land parcels held for development | land_parcel	7	6
Land held for development	$ 24,600,000	$ 20,100,000
Goodwill and Intangible Assets [Abstract]
Goodwill impairment loss	0	0
Goodwill	$ 3,500,000	3,487,000
Incentive Plans [Abstract]
Discount on market price on the date of grant	85.00%
Discount on market price on the date of exercise	85.00%
Expiration date	27 months
General and administrative	$ 34,511,000	32,992,000	31,309,000
Rental Income [Abstract]
Operating expense recoveries included in income from continuing operations	$ 81,100,000	$ 73,400,000	$ 66,000,000.0
Other Operating Income [Abstract]
Number of owned real estate properties to which property operating agreements between company and sponsoring health system is applicable | property	1	1	2
Federal Income Taxes [Abstract]
Percentage of distribution of taxable income for qualify as REIT	90.00%
Maximum [Member]
Real Estate Properties [Line Items]
Lessee, Operating Lease, Term of Contract	99 years
Minimum [Member]
Real Estate Properties [Line Items]
Lessee, Operating Lease, Term of Contract	40 years
Weighted Average [Member]
Real Estate Properties [Line Items]
Lessee, Operating Lease, Term of Contract	53 years 10 months 24 days
At Market Lease Intangibles [Member]
Real Estate Properties [Abstract]
Elimination of real estate lease intangibles against accumulated depreciation	$ 9,900,000	$ 10,200,000
Employee Stock Purchase Plan [Member]
Incentive Plans [Abstract]
General and administrative	300,000	200,000	$ 200,000
Tenant and Capital Improvements [Member]
Real Estate Properties [Abstract]
Fully depreciated tenant and capital improvements eliminated against accumulated depreciation	500,000	2,600,000
Forward Starting Interest Rate Swap [Member]
Derivative Instrument Detail [Abstract]
Accumulated other comprehensive income (loss), net of tax	$ 900,000	$ 1,300,000