Fair Value Measurement of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps	$ 19,192		$ 1,075
Interest rate swap liability	5,010		8,235
Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	15,972	[1]	12,957	[1]
Tenant receivables, net	31,006	[1]	25,038	[1]
Restricted cash and escrows	385	[1]	334	[1]
Interest rate swaps	19,192		1,075
Accounts payable and accrued expenses	22,229	[1]	23,113	[1]
Debt	1,823,175		1,416,525
Interest Rate Swap [Member] | Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swap liability	5,010		8,235
Level 1 [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	15,972	[1]	12,957	[1]
Tenant receivables, net	31,006	[1]	25,038	[1]
Restricted cash and escrows	385	[1]	334	[1]
Accounts payable and accrued expenses	22,229	[1]	23,113	[1]
Level 2 [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swaps	19,192		1,075
Debt	1,836,413		1,470,002
Level 2 [Member] | Interest Rate Swap [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate swap liability	$ 5,010		$ 8,235

[1] For the periods presented, the carrying value of these financial instruments approximates estimated fair value due to their short-term maturity.