Summary of Significant Accounting Policies - Narrative (Details) ft² in Millions		12 Months Ended
	May 05, 2015 USD ($)	Dec. 31, 2016 USD ($) ft² reporting_unit state property	Dec. 31, 2015 USD ($) mortgage_note_receivable employee property	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	May 06, 2016 USD ($)
Business Overview [Abstract]
Gross investment, amount, total		$ 3,600,000,000
Real estate properties and mortgages | property		202
Number of owned real estate properties | property		202
Number of states that the Company owns real estate in | state		27
Square footage of owned real estate properties | ft²		14.6
Approximate square feet for which Nationwide property management services provided by company | ft²		10.3
Segment Reporting [Abstract]
Number of Reporting Units | reporting_unit		1
Real Estate Properties [Abstract]
Total real estate properties		$ 3,628,221,000	$ 3,380,908,000
Maximum period up to which interest capitalize on properties in stabilization		1 year
Land Held for Development [Abstract]
Land held for development		$ 20,100,000	17,500,000
Goodwill and Intangible Assets [Abstract]
Goodwill impairment loss		0	0
Goodwill		3,487,000	$ 3,487,000
Defined Benefit Pension Plans [Abstract]
Number of employees covered by the Company's pension plan | employee			3
Total benefit obligation	$ 19,600,000	$ 0	$ 19,571,000	$ 16,473,000		$ 19,600,000
Current period charge	5,300,000		5,300,000
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 expense		$ 35,805,000	26,925,000	22,808,000
Revenue Recognition [Abstract]
Deferred revenue		32,400,000	36,400,000
Deferred revenue, tenant reimbursements		20,600,000	21,300,000
Rental Income [Abstract]
Operating expense recoveries included in income from continuing operations		$ 66,000,000	58,900,000	53,900,000
Additional rental income, net of reserves included in income from continuing operations			$ 0	700,000	$ 700,000
Mortgage Interest income [Abstract]
Number of Mortgage notes receivable outstanding with fixed interest rate | mortgage_note_receivable			1
Other Operating Income [Abstract]
Number of owned real estate properties to which property operating agreements between company and sponsoring health system is applicable | property		2	5
Federal Income Taxes [Abstract]
Percentage of distribution of taxable income for qualify as REIT		90.00%
At Market Lease Intangibles [Member]
Real Estate Properties [Abstract]
Elimination of real estate lease intangibles against accumulated depreciation		$ 6,700,000	$ 6,800,000
Level 1 [Member]
Fair Value Measurements [Abstract]
Impairment of property held for sale		100,000
Employee Stock Purchase Plan [Member]
Incentive Plans [Abstract]
General and administrative expense		200,000	200,000	$ 300,000
Tenant and Capital Improvements [Member]
Real Estate Properties [Abstract]
Fully depreciated tenant and capital improvements eliminated against accumulated depreciation		100,000	1,300,000
Accumulated Other Comprehensive Income (Loss) [Member]
Defined Benefit Pension Plans [Abstract]
Current period charge	$ 2,500,000		$ 2,500,000
Forward Starting Interest Rate Swap [Member]
Derivative Instrument Detail [Abstract]
Accumulated other comprehensive income (loss), net of tax		$ 1,400,000
Customer Concentration Risk [Member] | Revenue [Member]
Risks and Uncertainties [Abstract]
Concentration risk (percent)		9.80%	9.80%	10.50%