Deferred Leasing Costs and Acquisition-related Intangible Assets and Liabilities, net (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Dec. 31, 2012
Amortization for the period related to deferred leasing costs and acquisition-related intangibles
Amortization for the period related to deferred leasing costs and acquisition-related intangible assets	$ 13,232		$ 7,788
Deferred Leasing Costs [Member]
Amortization for the period related to deferred leasing costs and acquisition-related intangibles
Amortization for the period related to deferred leasing costs and acquisition-related intangible assets	7,844	[1]	4,498	[1]
Estimated annual amortization related to acquisition-related intangibles
Remaining 2013	18,417
2014	21,530
2015	17,558
2016	14,877
2017	12,311
Thereafter	24,149
Finite-lived intangible assets, net	108,842	[2]			106,644
Above-Market Leases [Member]
Amortization for the period related to deferred leasing costs and acquisition-related intangibles
Amortization for the period related to deferred leasing costs and acquisition-related intangible assets	1,438	[3]	1,371	[3]
Estimated annual amortization related to acquisition-related intangibles
Remaining 2013	3,939	[4]
2014	4,389	[4]
2015	2,586	[4]
2016	1,559	[4]
2017	1,225	[4]
Thereafter	919	[4]
Finite-lived intangible assets, net	14,617	[4]			15,797
In-Place Leases [Member]
Amortization for the period related to deferred leasing costs and acquisition-related intangibles
Amortization for the period related to deferred leasing costs and acquisition-related intangible assets	7,458	[1]	3,781	[1]
Estimated annual amortization related to acquisition-related intangibles
Remaining 2013	20,874
2014	18,012
2015	11,729
2016	8,613
2017	6,818
Thereafter	6,537
Finite-lived intangible assets, net	72,583	[2]			67,042
Below Market Ground Lease Obligation [Member]
Amortization for the period related to deferred leasing costs and acquisition-related intangibles
Amortization for the period related to deferred leasing costs and acquisition-related intangible assets	2	[5]	50	[5]
Estimated annual amortization related to acquisition-related intangibles
Remaining 2013	6	[6]
2014	8	[6]
2015	8	[6]
2016	8	[6]
2017	8	[6]
Thereafter	445	[6]
Finite-lived intangible assets, net	483	[6]			485
Below Market Leases [Member]
Amortization for the period related to deferred leasing costs and acquisition-related intangibles
Amortization for the period related to acquistion-related liabilities	(3,485)	[7]	(1,896)	[7]
Estimated annual amortization related to acquisition-related intangibles
Remaining 2013	9,847	[8]
2014	(11,512)	[8]
2015	(8,998)	[8]
2016	(6,814)	[8]
2017	(5,747)	[8]
Thereafter	(8,097)	[8]
Acquisition-related Intangible Liabilities, net	51,015	[2],[8],[9]			52,931	[9]
Above-Market Ground Lease Obligation [Member]
Amortization for the period related to deferred leasing costs and acquisition-related intangibles
Amortization for the period related to acquistion-related liabilities	(25)	[10]	(16)	[10]
Estimated annual amortization related to acquisition-related intangibles
Remaining 2013	76	[11]
2014	(101)	[11]
2015	(101)	[11]
2016	(101)	[11]
2017	(101)	[11]
Thereafter	(5,693)	[11]
Acquisition-related Intangible Liabilities, net	$ 6,173	[11],[9]			$ 6,198	[9]

[1] The amortization of deferred leasing costs and in-place leases is recorded to depreciation and amortization expense in the consolidated statements of operations for the periods presented.

[2] Balances and accumulated amortization amounts at March 31, 2013 reflect the write-off of the following fully amortized amounts at January 1, 2013: deferred leasing costs (approximately $7.0 million), above-market leases (approximately $0.6 million), in-place leases (approximately $10.3 million), and below-market leases (approximately $4.4 million).

[3] The amortization of above-market operating leases is recorded as a decrease to rental income in the consolidated statements of operations for the periods presented.

[4] Represents estimated annual amortization related to above-market operating leases. Amounts will be recorded as a decrease to rental income in the consolidated statements of operations.

[5] The amortization of the below-market ground lease obligation is recorded as an increase to ground lease expense in the consolidated statements of operations for the periods presented.

[6] Represents estimated annual amortization related to below−market ground lease obligations. Amounts will be recorded as an increase to ground lease expense in the consolidated statements of operations.

[7] The amortization of below−market operating leases is recorded as an increase to rental income in the consolidated statements of operations for the periods presented.

[8] Represents estimated annual amortization related to below-market operating leases. Amounts will be recorded as an increase to rental income in the consolidated statements of operations.

[9] Included in deferred revenue and acquisition-related intangible liabilities, net in the consolidated balance sheets.

[10] The amortization of the above-market ground lease obligation is recorded as a decrease to ground lease expense in the consolidated statements of operations for the periods presented.

[11] Represents estimated annual amortization related to above−market ground lease obligations. Amounts will be recorded as a decrease to ground lease expense in the consolidated statements of operations.