Summary of Significant Accounting Policies - Narrative (Details) ft² in Millions			12 Months Ended
		May. 05, 2015 USD ($)	Dec. 31, 2015 USD ($) ft² mortgage_note_receivable employee building reporting_unit state property	Dec. 31, 2014 USD ($) mortgage_note_receivable property	Dec. 31, 2013 USD ($) mortgage_note_receivable property
Business Overview [Abstract]
Gross investment, amount, total			$ 3,400,000,000
Real estate properties and mortgages | property			198
Number of owned real estate properties | property			198
Number of states that the Company owns real estate in | state			30
Square footage of owned real estate properties | ft²			14.3
Approximate square feet for which Nationwide property management services provided by company | ft²			9.8
Segment Reporting [Abstract]
Number of Reporting Units | reporting_unit			1
Real Estate Properties [Abstract]
Total real estate properties			$ 3,380,908,000	$ 3,258,279,000
Maximum period up to which interest capitalize on properties in stabilization			1 year
Land Held for Development [Abstract]
Land held for development			$ 17,500,000	17,100,000	$ 17,100,000
Fair Value Measurements [Abstract]
Number of impaired properties sold | building			1
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	$ 19,571,000	16,473,000	13,890,000
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			$ 26,925,000	22,808,000	23,704,000
Revenue Recognition [Abstract]
Deferred revenue			36,400,000	35,400,000
Deferred revenue, tenant reimbursements			21,300,000	22,400,000
Rental Income [Abstract]
Operating expense recoveries included in income from continuing operations			58,900,000	53,900,000	40,900,000
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	4
Other Operating Income [Abstract]
Number of owned real estate properties to which property operating agreements between company and sponsoring health system is applicable | property			5
Federal Income Taxes [Abstract]
Percentage of distribution of taxable income for qualify as REIT			90.00%
Mortgage Notes Receivable [Member]
Mortgage Notes and Notes Receivable [Abstract]
Number of mortgage notes receivable outstanding | mortgage_note_receivable			0	1
Mortgage notes receivable outstanding				$ 1,900,000
At Market Lease Intangibles [Member]
Real Estate Properties [Abstract]
Elimination of real estate lease intangibles against accumulated depreciation			$ 6,800,000	9,500,000
Level 1 [Member]
Fair Value Measurements [Abstract]
Other asset impairment charges			300,000
Level 3 [Member]
Fair Value Measurements [Abstract]
Other asset impairment charges			3,300,000
Employee Stock Purchase Plan [Member]
Incentive Plans [Abstract]
General and Administrative Expense			200,000	300,000	$ 300,000
Tenant and Capital Improvements [Member]
Real Estate Properties [Abstract]
Fully depreciated tenant and capital improvements eliminated against accumulated depreciation			1,300,000	400,000
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			1,600,000
Discontinued Operations [Member]
Real Estate Properties [Abstract]
Total real estate properties			1,772,000	$ 13,257,000
Fair Value Measurements [Abstract]
Number of impaired properties sold | property				3	2
Impairments Related to Property Held for Sale			700,000	$ 8,300,000	$ 6,200,000
Incentive Plans [Abstract]
General and Administrative Expense	[1]		0	$ 19,000	$ 26,000
Discontinued Operations [Member] | Level 3 [Member]
Fair Value Measurements [Abstract]
Impairments Related to Property Held for Sale			$ 700,000

[1] Total expenses for the years ended December 31, 2015, 2014 and 2013 included $0.1 million, $4.7 million and $8.7 million, respectively, related to properties sold.