Deferred Leasing Costs and Acquisition-related Intangible Assets and Liabilities, net (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
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 intangibles	$ 7,788		$ 6,594
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 intangibles	4,498	[1]	3,768	[1]
Estimated annual amortization related to acquisition-related intangibles
Remaining 2012	14,535
2013	17,541
2014	15,392
2015	11,828
2016	9,426
Thereafter	22,840
Total	91,562
Net (Below) 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 intangibles	(525)	[2]	653	[2]
Estimated annual amortization related to acquisition-related intangibles
Remaining 2012	(2,196)
2013	(3,091)
2014	(2,897)
2015	(2,285)
2016	(1,393)
Thereafter	(9,266)
Total	(21,128)	[3]
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 intangibles	3,781	[1]	2,173	[1]
Estimated annual amortization related to acquisition-related intangibles
Remaining 2012	11,111
2013	12,616
2014	9,173
2015	5,317
2016	2,903
Thereafter	6,520
Total	47,640
Net Below (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 deferred leasing costs and acquisition-related intangibles	34	[4]	0	[4]
Estimated annual amortization related to acquisition-related intangibles
Remaining 2012	103
2013	(63)
2014	(63)
2015	(63)
2016	(63)
Thereafter	(4,848)
Total	$ (4,997)	[5]

[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 net below−market operating leases is recorded as an increase to rental income for the three months ended March 31, 2012, and the amortization of the net above-market operating leases is recorded as a decrease to rental income for the three months ended March 31, 2011 in the consolidated statements of operations.

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

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

[5] Represents estimated annual net amortization related to (above)/below−market ground lease obligations. Amounts shown for 2012 represent net below−market ground lease obligations which will be recorded as an increase to ground lease expense in the consolidated statements of operations. Amounts shown for 2013−2016 and for the periods thereafter represent net above−market ground lease obligations which will be recorded as a decrease to ground lease expense in the consolidated statements of operations.