Debt (Narrative) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) properties $ / shares shares	Jun. 30, 2018 USD ($) shares	Jun. 30, 2019 USD ($) properties shares number_of_loans $ / shares	Jun. 30, 2018 USD ($) shares	Dec. 31, 2018 USD ($)
Document Period End Date			Jun. 30, 2019
Credit Facility, Current Revolving Borrowing Capacity		$ 550,000,000		$ 550,000,000
Derivative, Notional Amount	$ 610,000,000		$ 610,000,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			2000.00%
Debt Instrument, Variable Rate Basis, Minimum	24000.00%		24000.00%		25000.00%
Number of Real Estate Properties | properties	228		228
Debt Instrument, Convertible, Conversion Ratio			14.52
Debt Instrument, Convertible, Conversion Price | $ / shares	$ 68.86		$ 68.86
Debt Instrument, Convertible, Number of Equity Instruments | shares			1,742,736
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities | shares	199,492	24,251	211,503	12,126
Debt Instrument, Convertible, If-converted Value in Excess of Principal			$ 15,986,000
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	$ 883,000		883,000
Derivative, Fair Value, Net	(3,461,000)		(3,461,000)		$ 1,297,000
$250M Term Loan [Member]
Term Loans, Outstanding Balance	250,000,000		250,000,000
$300M Term Loan [Member]
Term Loans, Outstanding Balance	300,000,000		300,000,000
Debt Instrument, Name, Revolving Credit Facility [Member]
Unused balance of the unsecured revolving credit facility	$ 277,000,000		$ 277,000,000
Bank Term Loans [Member]
Debt Instrument, Basis Spread on Variable Rate			12600.00%
Debt Instrument, Name, HUD Mortgages [Member]
Number of Real Estate Properties | properties	10		10
Net Book Value of Real Estate Pledged Toward Mortgage	$ 50,007,000		$ 50,007,000
Debt Instrument, Name, HUD Mortgages [Member] | Minimum [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Interest Rate			4.30%
Debt Instrument, Name, HUD Mortgages [Member] | Maximum [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Interest Rate			4.40%
Debt Instrument, HUD Mortgages, 2049 Maturity [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Number of Loans | number_of_loans			9
Debt Instrument, HUD Mortgages, 2047 Maturity [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Number of Loans | number_of_loans			1
Debt Instrument, Name, Fannie Mae Term Loans [Member]
Number of Real Estate Properties	13		13
Net Book Value of Real Estate Pledged Toward Mortgage	$ 136,342,000		$ 136,342,000
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Face Amount of Mortgages	$ 78,084,000		$ 78,084,000
Debt Instrument, Interest Rate, Stated Percentage	3.79%		3.79%
Debt Instrument, Term			10 years
FNMA Berkadia Note [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Face Amount of Mortgages	$ 17,792,000		$ 17,792,000
Debt Instrument, Interest Rate, Stated Percentage	4.60%		4.60%
At Inception [Member]
Proceeds from convertible senior notes			$ 200,000,000
Debt Instrument, Convertible, Conversion Ratio			13.93
Debt Instrument, Convertible, Conversion Price | $ / shares	$ 71.81		$ 71.81
Debt Instrument, Convertible, Number of Equity Instruments | shares			2,785,200
Debt Instrument, Name, Convertible Senior Notes [Member]
Debt Instrument, Interest Rate, Stated Percentage	3.25%		3.25%
Convertible Debt Instrument, Conversion Ratio, Principal Amount, Basis			$ 1,000
Bickford Senior Living [Member]
Number of Real Estate Properties | properties	50		50
Middletown, OH [Member] | Bickford Senior Living [Member]
Noncash or Part Noncash Acquisition, Noncash Financial or Equity Instrument Consideration, Rate			2.90%
Noncash or Part Noncash Acquisition, Debt Assumed			$ 8,599,000
Noncash or Part Noncash Acquisition, Value of Liabilities Assumed			7,321,000
Interest Rate Swap(s), Date Entered, March & June 2019 [Member] | Debt Instrument, Name, Revolving Credit Facility [Member]
Derivative, Notional Amount	$ 60,000,000		60,000,000
Interest Rate Swap(s), Date Entered, March & June 2019 [Member] | Bank Term Loans [Member]
Derivative, Notional Amount	340,000,000		340,000,000
Interest Rate Swap, Date Entered, June 2013 [Member]
Derivative, Notional Amount	80,000,000		80,000,000
Interest Rate Swap, Date Entered, March 2014 [Member]
Derivative, Notional Amount	130,000,000		130,000,000
Interest Rate Swaps, Maturity Date, After June 2020 [Member]
Derivative, Notional Amount	$ 400,000,000		$ 400,000,000