Real Estate Intangibles (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended	3 Months Ended
	Jun. 30, 2012 year	Dec. 31, 2011 year	Jun. 30, 2012 Intangible Liability [Member]	Jun. 30, 2012 Intangible Asset [Member]	Jun. 30, 2012 In place lease intangibles [Member]	Dec. 31, 2011 In place lease intangibles [Member]	Jun. 30, 2012 Above market tenant leases [Member]	Dec. 31, 2011 Above market tenant leases [Member]	Jun. 30, 2012 Below market ground leases [Member]	Dec. 31, 2011 Below market ground leases [Member]	Jun. 30, 2012 Lease commissions [Member]	Dec. 31, 2011 Lease commissions [Member]	Jun. 30, 2012 Below market tenant leases [Member]	Dec. 31, 2011 Below market tenant leases [Member]	Jun. 30, 2012 Above market ground leases [Member]	Dec. 31, 2011 Above market ground leases [Member]
Assets:
Gross historical cost	$ 524,145	$ 428,199			$ 405,499	$ 332,645	$ 45,739	$ 35,973	$ 58,604	$ 51,316	$ 14,303	$ 8,265
Accumulated amortization	206,832	148,380
Net book value	317,313	279,819
Weighted-average amortization period in years	17 years 0 months	17 years 0 months
Liabilities:
Gross historical cost	78,278	72,304											72,384	67,284	5,894	5,020
Accumulated amortization	24,620	21,387
Net book value	53,658	50,917
Weighted-average amortization period in years	12.6	12.3
Estimated Aggregate Amortization Expense For Acquired Lease Intangibles Expected To Be Recognized [Line Items]
2012			3,450	67,938
2013			6,437	38,753
2014			5,979	25,899
2015			5,015	23,776
2016			4,657	25,016
Thereafter			28,120	135,931
Totals			$ 53,658	$ 317,313