Intangibles (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Intangible assets and liabilities
Intangible assets, gross	$ 830,408,000	$ 781,437,000
Intangible assets, accumulated amortization	(349,395,000)	(291,595,000)
Net intangible lease assets	481,013,000	489,842,000
Below market leases, Gross intangible lease liabilities	203,374,000	201,234,000
Above market ground lease, Gross intangible lease liabilities	6,121,000	6,121,000
Gross intangible lease liabilities	209,495,000	207,355,000
Intangible liabilities, accumulated amortization	(124,772,000)	(108,545,000)
Net intangible lease liabilities	84,723,000	98,810,000
Remaining weighted-average amortization period of intangible assets	14 years	15 years
Approximate remaining weighted-average amortization period of unfavorable market lease intangibles	9 years	9 years
Additional revenues from the amortization of net below market lease intangibles included in rental income	3,000,000	9,000,000	4,000,000
Additional expense from the amortization of net above market ground lease intangibles included in operating expenses	1,000,000	1,000,000	1,000,000
Additional expense from the amortization of lease-up and non-compete agreement intangibles included in depreciation and amortization expense	60,000,000	59,000,000	44,000,000
Estimated aggregate amortization of Intangible Assets
Estimated aggregate amortization of intangible assets, 2015	78,168,000
Estimated aggregate amortization of intangible assets, 2016	73,480,000
Estimated aggregate amortization of intangible assets, 2017	61,252,000
Estimated aggregate amortization of intangible assets, 2018	46,403,000
Estimated aggregate amortization of intangible assets, 2019	34,929,000
Estimated aggregate amortization of intangible assets, thereafter	186,781,000
Net intangible lease assets	481,013,000	489,842,000
Estimate aggregate amortization of Intangible Liabilities
Estimated aggregate amortization of intangible liabilities, 2015	17,069,000
Estimated aggregate amortization of intangible liabilities, 2016	16,528,000
Estimated aggregate amortization of intangible liabilities, 2017	14,101,000
Estimated aggregate amortization of intangible liabilities, 2018	11,406,000
Estimated aggregate amortization of intangible liabilities, 2019	8,800,000
Estimated aggregate amortization of intangible liabilities, thereafter	16,819,000
Net intangible lease liabilities	84,723,000	98,810,000
Lease-up intangibles
Intangible assets and liabilities
Intangible assets, gross	608,323,000	578,143,000
Tenant leases | Above market
Intangible assets and liabilities
Intangible assets, gross	163,146,000	144,355,000
Ground leases | Below market
Intangible assets and liabilities
Intangible assets, gross	$ 58,939,000	$ 58,939,000