Mortgages Payable (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Mortgages Payable
Assumed mortgages payable	$ 110,500,000	$ 67,400,000
Debt instrument
Remaining Principal Balance	165,927,000	67,150,000
Amortized Premium (Discount) Balance	9,941,000	631,000
Mortgage Payable Balance	175,868,000	67,781,000
Note receivable acquired in connection with 2011 acquisition		8,800,000
Mortgages Payable
Debt instrument
Number of mortgages repaid	1
Amount repaid	10,700,000
Net premiums recorded upon assumption of mortgages	10,000,000	820,000
Deferred financing costs incurred	1,100,000	917,000
Remaining balance of deferred financing costs at period end	1,541,000	751,000
Mortgages maturing 5/6/12
Debt instrument
Stated Interest Rate (as a percent)		5.90%
Effective Interest Rate (as a percent)		5.20%
Remaining Principal Balance		10,664,000
Amortized Premium (Discount) Balance		26,000
Mortgage Payable Balance		10,690,000
Mortgages maturing 12/1/13
Debt instrument
Stated Interest Rate (as a percent)	6.30%	6.30%
Effective Interest Rate (as a percent)	4.60%	4.60%
Remaining Principal Balance	11,987,000	12,410,000
Amortized Premium (Discount) Balance	172,000	314,000
Mortgage Payable Balance	12,159,000	12,724,000
Mortgages one maturing 12/28/13
Debt instrument
Stated Interest Rate (as a percent)	8.30%	8.30%
Effective Interest Rate (as a percent)	8.30%	8.30%
Remaining Principal Balance	4,510,000	4,510,000
Mortgage Payable Balance	4,510,000	4,510,000
Mortgages two maturing 12/28/13
Debt instrument
Stated Interest Rate (as a percent)	8.30%	8.30%
Effective Interest Rate (as a percent)	8.30%	8.30%
Remaining Principal Balance	4,270,000	4,270,000
Mortgage Payable Balance	4,270,000	4,270,000
Mortgages maturing 9/1/14
Debt instrument
Stated Interest Rate (as a percent)	6.30%	6.30%
Effective Interest Rate (as a percent)	5.10%	5.10%
Remaining Principal Balance	11,509,000	11,671,000
Amortized Premium (Discount) Balance	196,000	359,000
Mortgage Payable Balance	11,705,000	12,030,000
Mortgages maturing 6/10/15
Debt instrument
Stated Interest Rate (as a percent)	4.70%	4.70%
Effective Interest Rate (as a percent)	4.80%	4.80%
Remaining Principal Balance	23,625,000	23,625,000
Amortized Premium (Discount) Balance	(48,000)	(68,000)
Mortgage Payable Balance	23,577,000	23,557,000
Floating variable interest rate, variable rate basis	1 month LIBOR	1 month LIBOR
Floating variable interest rate, basis spread on variable rate (as a percent)	4.50%	4.50%
Maximum interest rate (as a percent)	5.50%	5.50%
Mortgages maturity 1/10/16
Debt instrument
Stated Interest Rate (as a percent)	6.00%
Effective Interest Rate (as a percent)	3.70%
Remaining Principal Balance	12,982,000
Amortized Premium (Discount) Balance	794,000
Mortgage Payable Balance	13,776,000
Mortgages maturing 1/8/17
Debt instrument
Stated Interest Rate (as a percent)	5.70%
Effective Interest Rate (as a percent)	3.80%
Remaining Principal Balance	6,883,000
Amortized Premium (Discount) Balance	454,000
Mortgage Payable Balance	7,337,000
Mortgages maturing 2/8/17
Debt instrument
Stated Interest Rate (as a percent)	5.80%
Effective Interest Rate (as a percent)	4.00%
Remaining Principal Balance	29,510,000
Amortized Premium (Discount) Balance	1,829,000
Mortgage Payable Balance	31,339,000
Mortgages maturing 6/6/17
Debt instrument
Stated Interest Rate (as a percent)	5.70%
Effective Interest Rate (as a percent)	2.70%
Remaining Principal Balance	10,150,000
Amortized Premium (Discount) Balance	1,201,000
Mortgage Payable Balance	11,351,000
Mortgages maturing 10/1/20
Debt instrument
Stated Interest Rate (as a percent)	6.00%
Effective Interest Rate (as a percent)	4.20%
Remaining Principal Balance	8,765,000
Amortized Premium (Discount) Balance	907,000
Mortgage Payable Balance	9,672,000
Mortgages maturing 9/3/21
Debt instrument
Stated Interest Rate (as a percent)	2.60%
Effective Interest Rate (as a percent)	4.00%
Remaining Principal Balance	8,359,000
Amortized Premium (Discount) Balance	(771,000)
Mortgage Payable Balance	7,588,000
Floating variable interest rate, variable rate basis	1 month LIBOR
Floating variable interest rate, basis spread on variable rate (as a percent)	2.40%
Assumed interest rate swap fixed interest rate (as a percent)	6.00%
Mortgages maturing 7/8/22
Debt instrument
Stated Interest Rate (as a percent)	6.40%
Effective Interest Rate (as a percent)	4.00%
Remaining Principal Balance	29,308,000
Amortized Premium (Discount) Balance	4,675,000
Mortgage Payable Balance	33,983,000
Mortgages maturing 4/1/25
Debt instrument
Stated Interest Rate (as a percent)	6.90%
Effective Interest Rate (as a percent)	5.10%
Remaining Principal Balance	4,069,000
Amortized Premium (Discount) Balance	532,000
Mortgage Payable Balance	4,601,000
Mortgages maturing 12/28/13
Debt instrument
Note receivable acquired in connection with 2011 acquisition	$ 8,800,000	$ 8,800,000
Assumed note receivable stated interest rate (as a percent)	8.14%	8.14%