Deferred Leasing Costs and Acquisition-related Intangible Assets and Liabilities, net (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 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	$ 12,661		$ 9,716		$ 37,343		$ 24,461
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	6,945	[1]	5,238	[1]	20,882	[1]	14,126	[1]
Estimated annual amortization related to acquisition-related intangibles
Remaining 2013	6,384				6,384
2014	23,533				23,533
2015	19,669				19,669
2016	16,920				16,920
2017	14,468				14,468
Thereafter	29,692				29,692
Finite-lived intangible assets, net	110,666				110,666				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	1,417	[2]	1,459	[2]	4,214	[2]	4,205	[2]
Estimated annual amortization related to acquisition-related intangibles
Remaining 2013	1,367	[3]			1,367	[3]
2014	4,837	[3]			4,837	[3]
2015	3,035	[3]			3,035	[3]
2016	2,007	[3]			2,007	[3]
2017	1,690	[3]			1,690	[3]
Thereafter	1,868	[3]			1,868	[3]
Finite-lived intangible assets, net	14,804	[3]			14,804	[3]			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	7,677	[1]	6,479	[1]	22,546	[1]	14,858	[1]
Estimated annual amortization related to acquisition-related intangibles
Remaining 2013	6,549				6,549
2014	19,053				19,053
2015	12,676				12,676
2016	9,445				9,445
2017	7,744				7,744
Thereafter	8,669				8,669
Finite-lived intangible assets, net	64,136				64,136				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	[4]	52	[4]	6	[4]	153	[4]
Estimated annual amortization related to acquisition-related intangibles
Remaining 2013	2	[5]			2	[5]
2014	8	[5]			8	[5]
2015	8	[5]			8	[5]
2016	8	[5]			8	[5]
2017	8	[5]			8	[5]
Thereafter	445	[5]			445	[5]
Finite-lived intangible assets, net	479	[5]			479	[5]			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	(3,355)	[6]	(3,487)	[6]	(10,229)	[6]	(8,821)	[6]
Estimated annual amortization related to acquisition-related intangibles
Remaining 2013	(3,201)	[7]			(3,201)	[7]
2014	(11,903)	[7]			(11,903)	[7]
2015	(9,385)	[7]			(9,385)	[7]
2016	(7,195)	[7]			(7,195)	[7]
2017	(6,127)	[7]			(6,127)	[7]
Thereafter	(9,081)	[7]			(9,081)	[7]
Acquisition-related Intangible Liabilities, net	(46,892)	[7],[8]			(46,892)	[7],[8]			(52,931)	[8]
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)	[9]	(25)	[9]	(76)	[9]	(60)	[9]
Estimated annual amortization related to acquisition-related intangibles
Remaining 2013	(25)	[10]			(25)	[10]
2014	(101)	[10]			(101)	[10]
2015	(101)	[10]			(101)	[10]
2016	(101)	[10]			(101)	[10]
2017	(101)	[10]			(101)	[10]
Thereafter	(5,693)	[10]			(5,693)	[10]
Acquisition-related Intangible Liabilities, net	$ (6,122)	[10],[8]			$ (6,122)	[10],[8]			$ (6,198)	[8]

[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] 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.

[3] 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.

[4] 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.

[5] 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.

[6] 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.

[7] 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.

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

[9] 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.

[10] 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.