Debt (Details) (USD $)	0 Months Ended	12 Months Ended										0 Months Ended										12 Months Ended		0 Months Ended			12 Months Ended		0 Months Ended		12 Months Ended		0 Months Ended								0 Months Ended	12 Months Ended			0 Months Ended												0 Months Ended	12 Months Ended	0 Months Ended				0 Months Ended		12 Months Ended				12 Months Ended	0 Months Ended					12 Months Ended				0 Months Ended
	Sep. 14, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Minimum	Dec. 31, 2012 Minimum	Dec. 31, 2013 Maximum	Dec. 31, 2012 Maximum	Dec. 31, 2013 Mortgage notes payable	Dec. 31, 2012 Mortgage notes payable	Dec. 31, 2013 Sun Life	Dec. 31, 2012 Sun Life	Oct. 07, 2013 Bank of America Unsecured Credit Facility and Unsecured Term Loan	Oct. 07, 2013 Bank of America Unsecured Credit Facility and Unsecured Term Loan Original Terms	Oct. 07, 2013 Bank of America Unsecured Credit Facility and Unsecured Term Loan Base Rate Original Terms	Oct. 07, 2013 Bank of America Unsecured Credit Facility and Unsecured Term Loan Eurodollar Rate Original Terms	Oct. 07, 2013 Bank of America Unsecured Credit Facility and Unsecured Term Loan Minimum Base Rate Original Terms	Oct. 07, 2013 Bank of America Unsecured Credit Facility and Unsecured Term Loan Minimum Eurodollar Rate Original Terms	Oct. 07, 2013 Bank of America Unsecured Credit Facility and Unsecured Term Loan Maximum Base Rate Original Terms	Oct. 07, 2013 Bank of America Unsecured Credit Facility and Unsecured Term Loan Maximum Eurodollar Rate Original Terms	Dec. 31, 2013 Webster Bank, maturity date Aug 4, 2016	Dec. 31, 2012 Webster Bank, maturity date Aug 4, 2016	Dec. 31, 2013 Bank of America Unsecured Credit Facility, due on September 10, 2016	Dec. 31, 2012 Bank of America Unsecured Credit Facility, due on September 10, 2016	Oct. 07, 2013 Bank of America Unsecured Credit Facility, due on September 10, 2016 Amended Terms	Oct. 07, 2013 Bank of America Unsecured Credit Facility, due on September 10, 2016 Base Rate Amended Terms	Oct. 07, 2013 Bank of America Unsecured Credit Facility, due on September 10, 2016 Eurodollar Rate Amended Terms	Dec. 31, 2013 Bank of America Unsecured Credit Facility, due on September 10, 2016 Minimum	Dec. 31, 2012 Bank of America Unsecured Credit Facility, due on September 10, 2016 Minimum	Oct. 07, 2013 Bank of America Unsecured Credit Facility, due on September 10, 2016 Minimum Base Rate Amended Terms	Oct. 07, 2013 Bank of America Unsecured Credit Facility, due on September 10, 2016 Minimum Eurodollar Rate Amended Terms	Dec. 31, 2013 Bank of America Unsecured Credit Facility, due on September 10, 2016 Maximum	Dec. 31, 2012 Bank of America Unsecured Credit Facility, due on September 10, 2016 Maximum	Oct. 07, 2013 Bank of America Unsecured Credit Facility, due on September 10, 2016 Maximum Base Rate Amended Terms	Oct. 07, 2013 Bank of America Unsecured Credit Facility, due on September 10, 2016 Maximum Eurodollar Rate Amended Terms	Dec. 31, 2013 Union Fidelity	Dec. 31, 2012 Union Fidelity	Dec. 31, 2013 Webster Bank, maturity date May 29, 2017	Dec. 31, 2012 Webster Bank, maturity date May 29, 2017	Dec. 31, 2013 Webster Bank, maturity date May 31, 2017	Dec. 31, 2012 Webster Bank, maturity date May 31, 2017	Sep. 14, 2012 Bank of America Unsecured Term Loan, due on September 10, 2017	Dec. 31, 2013 Bank of America Unsecured Term Loan, due on September 10, 2017	Dec. 31, 2012 Bank of America Unsecured Term Loan, due on September 10, 2017	Sep. 10, 2012 Bank of America Unsecured Term Loan, due on September 10, 2017	Oct. 07, 2013 Bank of America Unsecured Term Loan, due on September 10, 2017 Base Rate Amended Terms	Oct. 07, 2013 Bank of America Unsecured Term Loan, due on September 10, 2017 Eurodollar Rate Amended Terms	Oct. 07, 2013 Bank of America Unsecured Term Loan, due on September 10, 2017 Minimum Base Rate Amended Terms	Oct. 07, 2013 Bank of America Unsecured Term Loan, due on September 10, 2017 Minimum Eurodollar Rate Amended Terms	Oct. 07, 2013 Bank of America Unsecured Term Loan, due on September 10, 2017 Maximum Base Rate Amended Terms	Oct. 07, 2013 Bank of America Unsecured Term Loan, due on September 10, 2017 Maximum Eurodollar Rate Amended Terms	Dec. 31, 2013 CIGNA-1 Facility	Dec. 31, 2012 CIGNA-1 Facility	Dec. 31, 2013 CIGNA-2 Facility	Dec. 31, 2012 CIGNA-2 Facility	Dec. 31, 2013 CIGNA-3 Facility	Dec. 31, 2012 CIGNA-3 Facility	Feb. 14, 2013 Wells Fargo, Unsecured Term Loan, due on February 14, 2020	Dec. 31, 2013 Wells Fargo, Unsecured Term Loan, due on February 14, 2020	Feb. 14, 2013 Wells Fargo, Unsecured Term Loan, due on February 14, 2020 LIBOR	Dec. 31, 2013 Wells Fargo, CMBS Loan	Dec. 31, 2012 Wells Fargo, CMBS Loan	Nov. 08, 2012 Wells Fargo, CMBS Loan	Oct. 07, 2013 Unsecured Credit Facility	Sep. 10, 2012 Unsecured Credit Facility	Dec. 31, 2013 Unsecured Credit Facility Minimum	Dec. 31, 2013 Unsecured Credit Facility Maximum	Sep. 10, 2012 Swing line loans	Sep. 10, 2012 Letter of credit	Dec. 31, 2013 CIGNA-1, CIGNA-2, and CIGNA-3 facilities item	Sep. 10, 2012 Wells Fargo Master Loan-Fixed Amount	Aug. 15, 2012 Wells Fargo Master Loan-Fixed Amount	Sep. 10, 2012 Credit Facility	Oct. 07, 2013 Unsecured Term Loan	Sep. 10, 2012 Unsecured Term Loan	Dec. 31, 2013 Unsecured Term Loan Minimum	Dec. 31, 2012 Unsecured Term Loan Minimum	Dec. 31, 2013 Unsecured Term Loan Maximum	Dec. 31, 2012 Unsecured Term Loan Maximum	Jun. 27, 2012 Bank of America, N.A.
Debt instruments
Interest rate base		One-month LIBOR	One-month LIBOR											Base rate	one month-LIBOR							LIBOR			Base rate	one month-LIBOR																LIBOR			Base rate	one month-LIBOR												LIBOR	one-month LIBOR
Interest rate margin (as a percent)																0.65%	1.65%	1.25%	2.25%			1.45%					1.45%	1.45%	0.45%	1.45%	1.65%	1.65%	1.05%	2.05%								1.40%					0.40%	1.40%	1.00%	2.00%								2.15%	2.70%																1.40%	1.40%	1.65%	1.65%
Interest Rate (as a percent)										6.05%										4.22%															5.81%		3.66%		3.64%												6.50%		5.75%		5.88%					4.31%																			7.05%
One-month LIBOR rate (as a percent)		0.1677%	0.2087%
Principal outstanding		$ 556,091,000	$ 479,215,000					$ 225,591,000	$ 229,915,000	$ 3,817,000	$ 4,079,000									$ 5,834,000	$ 5,984,000	$ 80,500,000	$ 99,300,000												$ 6,551,000	$ 6,898,000	$ 3,121,000	$ 3,203,000	$ 3,360,000	$ 3,450,000		$ 150,000,000	$ 150,000,000								$ 58,874,000	$ 59,645,000	$ 59,990,000	$ 60,863,000	$ 16,879,000	$ 17,097,000		$ 100,000,000		$ 67,165,000	$ 68,696,000	$ 68,800,000
Repayment of principal outstanding																																																																						18,700,000									8,100,000
New or additional borrowings																																																									150,000,000
Unamortized fair market value premium		288,000						288,000		200,000	200,000																								100,000	200,000
Portion of unsecured term loan swapped from LIBOR for fixed rate	100,000,000																																									100,000,000																125,000,000
Unused commitment fees																						600,000	100,000																																		300,000															2,500,000
Unsecured Term Loan																																									150,000,000			150,000,000														150,000,000																150,000,000
Additional borrowing capacity																																																									250,000,000									300,000,000
Variable rate received under agreement																																									One-month LIBOR	One-month LIBOR
Consolidated leverage ratio																																																																		0.60
Secured leverage ratio																																																																		0.45
Unencumbered leverage ratio																																																																		0.60
Secured recourse debt ratio																																																																		7.50
Fixed charge ratio																																																																	1.50
Discount rate at which cash flows are discounted (as a percent)			11.40%	1.57%	1.86%	5.24%	4.64%
Fair value								228,996,000	242,175,000													80,500,000	99,300,000																			148,781,000	150,000,000															97,302,000
Remaining borrowing capacity																																										0									0		2,900,000		47,900,000			50,000,000
Maximum borrowing capacity																						119,300,000																																										200,000,000			10,000,000	10,000,000
Gain (loss) on early extinguishment of the loan			(929,000)																																																																												18,000
Service coverage ratio after to satisfaction of an appraisal condition																																																																		1.6
Pre-payment penalties																																																																						0		0							0
Loss on early extinguishment of credit facility																																																																						400,000		500,000
Unused commitment fee (as a percent)																																																									0.35%
Unused commitment fee when usage more than 50 % (as a percent)													0.25%											0.20%
Unused commitment fee when usage less than 50 % (as a percent)													0.35%											0.25%
Deferred financing fees, net		5,467,000	4,704,000																																																						1,400,000						300,000										200,000
Deferred financing fees amortization period																																																									7 years						3 years									5 years	4 years
Deferred financing fees expensed as a loss on extinguishment of debt												0
Deferred annual fees																																																									50,000
Deferred annual fees amortization period																																																									1 year
Prepayment of debt																																																																							105,000,000
Number of properties held as collateral that are cross-collateralized																																																																					21
Net book value of collateralized properties for debt arrangements		262,700,000	269,100,000
Aggregate future principal payments of mortgage notes payable, Unsecured credit facility
2014								4,447,000
2015								4,688,000
2016								93,777,000
2017								165,506,000
2018								113,377,000
Thereafter								174,008,000
Total aggregate principal payments								555,803,000
Unamortized fair market value premium		288,000						288,000		200,000	200,000																								100,000	200,000
Total carrying value of debt		$ 225,591,000	$ 229,915,000					$ 556,091,000