Real Estate Intangibles (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Assets
Other Finite-Lived Intangible Assets, Gross	$ 1,070,754,000	$ 673,684,000
Accumulated amortization	(571,008,000)	(257,242,000)
Net book value	499,746,000	416,442,000
Weighted-average amortization period in years	16 years 8 months	16 years 5 months
Liabilities
Real estate intangible liabilities, Gross	85,871,000	86,526,000
Accumulated amortization	(34,434,000)	(27,753,000)
Net book value	51,437,000	58,773,000
Weighted-average amortization period in years	14 years 4 months	14 years 4 months
In place lease intangibles [Member]
Assets
Other Finite-Lived Intangible Assets, Gross	937,357,000	541,729,000
Above market tenant leases [Member]
Assets
Other Finite-Lived Intangible Assets, Gross	55,939,000	56,086,000
Below market ground leases [Member]
Assets
Other Finite-Lived Intangible Assets, Gross	59,165,000	61,450,000
Lease commissions [Member]
Assets
Other Finite-Lived Intangible Assets, Gross	18,293,000	14,419,000
Gross historical cost [Member]
Assets
Other Finite-Lived Intangible Assets, Gross	1,070,754,000	673,684,000
Below market tenant leases [Member]
Liabilities
Real estate intangible liabilities, Gross	76,381,000	77,036,000
Above market ground leases [Member]
Liabilities
Real estate intangible liabilities, Gross	$ 9,490,000	$ 9,490,000