Debt (Narrative) (Details) (USD $)	6 Months Ended				6 Months Ended			6 Months Ended							6 Months Ended
	Jun. 30, 2014 properties	Jun. 30, 2013	Mar. 27, 2014	Dec. 31, 2013	Jun. 30, 2014 Debt Instrument, Name, Convertible Senior Notes [Member]	Jun. 30, 2014 Debt Instrument, Name, Revolving Credit Facility [Member]	Jun. 30, 2014 Debt Instrument Name, Old Revolving Credit Facility [Member]	Jun. 30, 2014 Debt Instrument Name, $130m Term Loan - June 2020 Maturity [Member]	Jun. 30, 2014 Debt Instrument Name, $120m Term Loans - June 2020 Maturity [Member]	Jun. 30, 2014 Debt Instrument, Name, Fannie Mae (A) [Member]	Jun. 30, 2014 Debt Instrument, Name, Fannie Mae (B) [Member]	Jun. 30, 2014 Interest Rate Swap, Date Entered, March 2014 [Member]	Jun. 30, 2014 Interest Rate Swap, Date Entered, May 2012 [Member]	Jun. 30, 2014 Interest Rate Swap, Date Entered, June 2013 [Member]	Jun. 30, 2014 Allocated to Debt [Member] Debt Instrument, Name, Convertible Senior Notes [Member]	Jun. 30, 2014 Allocated to Equity [Member] Debt Instrument, Name, Convertible Senior Notes [Member]	Jul. 31, 2014 Subsequent Event [Member] Debt Instrument, Name, HUD Mortgages [Member] properties
Mortgage Loans on Real Estate, Face Amount of Mortgages																	$ 29,199,000
Proceeds from convertible senior notes	200,000,000	0
Line of Credit Facility, Maximum Borrowing Capacity	700,000,000						620,000,000
Long-term Debt	79,503,000			80,080,000						70,613,000	7,185,000
Debt Instrument, Interest Rate, Stated Percentage					3.25%					6.85%	7.17%						4.30%
Number of Additional Properties, HUD Mortgage Security																	2
Debt Instrument, Convertible, Conversion Ratio	13.926
Convertible Debt Instrument, Conversion Ratio, Principal Amount, Basis	1,000
Debt Instrument, Convertible, Conversion Price	$ 71.81
Debt Instrument, Convertible, Number of Equity Instruments	2,785,200
Convertible Debt	192,516,000		192,238,000	0
Debt Instrument, Convertible, Carrying Amount of Equity Component	7,762,000
Debt Instrument, Interest Rate, Effective Percentage	3.90%
Debt Issuance Cost					6,055,000										5,789,000	267,000
Term Loans, Outstanding Balance								130,000,000	120,000,000
Debt Maturity, Extension Option, Number Of Years						1
Credit Facility, Current Revolving Borrowing Capacity	450,000,000
Number of basis points over LIBOR						150		175	175
Credit Facility Expansion Amount	130,000,000
Unused balance of the unsecured revolving credit facility						334,000,000
Debt Instrument, Unused Borrowing Capacity, Fee, Basis Points	40
Derivative, Fixed Interest Rate												3.91%	3.29%	3.86%
Derivative, Notional Amount												130,000,000	40,000,000	80,000,000
Number of Real Estate Properties	162																7
Anticipated Total HUD Proceeds, Current Year																	$ 38,000,000