Debt (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) properties $ / shares shares	Sep. 30, 2018 shares	Sep. 30, 2019 USD ($) properties shares number_of_loans $ / shares	Sep. 30, 2018 shares	Dec. 31, 2018 USD ($)
Debt Leverage Limit, Coupon Change, Trigger			50.00%
Document Period End Date			Sep. 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	20200.00%		20200.00%		25000.00%
Long-term Line of Credit	$ 250,000,000		$ 250,000,000		$ 84,000,000
Number of Real Estate Properties | properties	222		222
Debt Instrument, Convertible, Conversion Ratio			14.57
Debt Instrument, Convertible, Conversion Price | $ / shares	$ 68.63		$ 68.63
Debt Instrument, Convertible, Number of Equity Instruments | shares			1,748,616
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities | shares	275,824	149,153	232,943	57,802
Debt Instrument, Convertible, If-converted Value in Excess of Principal			$ 24,068,000
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	$ 2,217,000		2,217,000
Derivative, Fair Value, Net	(4,810,000)		(4,810,000)		$ 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]
Debt Instrument, Basis Spread on Variable Rate			12000.00%
Unused balance of the unsecured revolving credit facility	300,000,000		$ 300,000,000
Bank Term Loans [Member]
Debt Instrument, Basis Spread on Variable Rate			13200.00%
Variable Interest Rate Debt [Member]
Long-term Line of Credit	$ 190,000,000		$ 190,000,000
Debt Instrument, Name, HUD Mortgages [Member]
Number of Real Estate Properties | properties	10		10
Net Book Value of Real Estate Pledged Toward Mortgage	$ 49,577,000		$ 49,577,000
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	$ 135,267,000		$ 135,267,000
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	$ 17,709,000		$ 17,709,000
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	51		51
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			$ 8,546,000
Noncash or Part Noncash Acquisition, Value of Liabilities Assumed			7,288,000
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