Deferred Leasing Intangibles (Details) (USD $)													3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 In-place leases	Dec. 31, 2012 In-place leases	Mar. 31, 2013 Above market leases	Dec. 31, 2012 Above market leases	Mar. 31, 2013 Tenant relationships	Dec. 31, 2012 Tenant relationships	Mar. 31, 2013 Leasing commissions	Dec. 31, 2012 Leasing commissions	Mar. 31, 2013 Below market leases	Dec. 31, 2012 Below market leases	Mar. 31, 2013 In-place leases, lease commissions and tenant relationships	Mar. 31, 2012 In-place leases, lease commissions and tenant relationships	Mar. 31, 2013 Above and below market leases	Mar. 31, 2012 Above and below market leases
Deferred leasing intangibles, assets
Gross			$ 115,852,000	$ 108,363,000	$ 51,064,000	$ 50,699,000	$ 64,834,000	$ 61,050,000	$ 25,664,000	$ 23,376,000
Less: Accumulated amortization			(34,238,000)	(28,289,000)	(12,199,000)	(10,362,000)	(13,837,000)	(11,298,000)	(6,897,000)	(5,984,000)
Net	190,243,000	187,555,000	81,614,000	80,074,000	38,865,000	40,337,000	50,997,000	49,752,000	18,767,000	17,392,000
Deferred leasing intangibles, liabilities
Gross											10,329,000	9,878,000
Less: Accumulated amortization											(3,477,000)	(3,007,000)
Net	6,852,000	6,871,000
Amortization expense													9,400,000	5,000,000
Net decrease to rental revenues related to net amortization of above (below) market leases															(1,400,000)	(1,200,000)
Estimated Net Amortization of In-Place Leases, Leasing Commissions and Tenant Relationships
Remainder of 2013													35,334,000
2014													29,953,000
2015													23,589,000
2016													19,642,000
2017													15,405,000
Net Decrease to Rental Income Related to Above and Below Market Leases
Remainder of 2013															5,285,000
2014															4,802,000
2015															5,088,000
2016															4,755,000
2017															$ 3,525,000