Debt Obligations (Details) (USD $)	12 Months Ended			1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 31, 2015
Debt Obligations
Amount outstanding under Unsecured Credit Agreement		$ 21,000,000
Proceeds from issuance of senior unsecured notes	30,000,000	70,000,000	85,800,000
Amount outstanding Senior Unsecured Notes	281,633,000	255,800,000
Scheduled Principal Payments
Total	281,633,000
2015	29,166,000
2016	26,667,000
2017	26,167,000
2018	28,167,000
2019	25,666,000
Thereafter	145,800,000
Line of Credit [Member]
Debt Obligations
Maximum availability under Unsecured Credit Agreement	400,000,000
Possible total maximum availability under Unsecured Credit Agreement	600,000,000
Decrease in drawn pricing, basis point (as a percent)	0.25%
Extension of maturity date	1 year
Description of interest rate	LIBOR
Basis spread over base rate (as a percent)	1.15%
Unused commitment fee (as a percent)	0.25%
Maximum ratio of total indebtedness to total asset value	0.5
Maximum ratio of secured debt to total asset value	0.35
Maximum ratio of unsecured debt to the value of the unencumbered asset pool	0.6
Minimum ratio of EBITDA to fixed charges	1.50
Amount borrowed	37,500,000			18,000,000
Repayment amount	58,500,000
Amount outstanding under Unsecured Credit Agreement	0			18,000,000
Amount available for borrowing under Unsecured Credit Agreement	400,000,000			382,000,000
Line of Credit [Member] | Subsequent Event [Member]
Debt Obligations
Amount borrowed	18,000,000
Amount outstanding under Unsecured Credit Agreement	18,000,000
Amount available for borrowing under Unsecured Credit Agreement	382,000,000
Senior Unsecured Debt [Member]
Debt Obligations
Amount outstanding Senior Unsecured Notes	281,633,000	255,800,000
Weighted average interest rate (as a percent)	4.81%	4.85%
Repayments of debt	4,167,000
Scheduled Principal Payments
Total	281,633,000
2015	29,166,000
2016	26,667,000
2017	26,167,000
2018	28,167,000
2019	25,666,000
Thereafter	145,800,000
Senior Unsecured Term Note 4.50 Percent Due 31 July 2026 [Member]
Debt Obligations
Proceeds from issuance of senior unsecured notes	30,000,000
Stated interest rate (as a percent)	4.50%
Senior Unsecured Term Notes 3.99 Percent Due 20 November 2021 [Member]
Debt Obligations
Proceeds from issuance of senior unsecured notes		70,000,000
Stated interest rate (as a percent)		3.99%
Senior Unsecured Term Notes 5.0 Percent Due 19, July 2024 [Member]
Debt Obligations
Proceeds from issuance of senior unsecured notes			85,800,000
Stated interest rate (as a percent)			5.00%
Maturity Period			12 years
Senior Unsecured Term Notes 4.80 Percent Due 20 July 2021 [Member]
Debt Obligations
Proceeds from issuance of senior unsecured notes			50,000,000
Stated interest rate (as a percent)			4.80%
Bonds [Member]
Debt Obligations
Face amount of debt	1,400,000
Repayments of debt	$ 635,000	$ 600,000
Number of assisted living properties securing debt instruments	5