Real Estate Intangibles

3 Months Ended

Mar. 31, 2012

4. Real Estate Intangibles

The following is a summary of our real estate intangibles, excluding those classified as held for sale, as of the dates indicated (dollars in thousands):

		March 31, 2012		December 31, 2011
Assets:
	In place lease intangibles	$	385,367	$	332,645
	Above market tenant leases		42,597		35,973
	Below market ground leases		58,604		51,316
	Lease commissions		10,821		8,265
	Gross historical cost		497,389		428,199
	Accumulated amortization		(176,365)		(148,380)
	Net book value	$	321,024	$	279,819

	Weighted-average amortization period in years		16.6		17.0

Liabilities:
	Below market tenant leases	$	70,304	$	67,284
	Above market ground leases		5,894		5,020
	Gross historical cost		76,198		72,304
	Accumulated amortization		(22,971)		(21,387)
	Net book value	$	53,227	$	50,917

	Weighted-average amortization period in years		12.6		12.3

The following is a summary of real estate intangible amortization for the periods presented (in thousands):

	Three Months Ended March 31,
	2012		2011
Rental income related to above/below market tenant leases, net	$	552	$	926
Property operating expenses related to above/below market ground leases, net		(300)		(268)
Depreciation and amortization related to in place lease intangibles and lease commissions		(27,605)		(14,610)

The future estimated aggregate amortization of intangible assets and liabilities is as follows for the periods presented (in thousands):

		Assets		Liabilities
2012	$	83,732	$	5,040
2013		39,211		6,191
2014		23,784		5,734
2015		21,440		4,750
2016		23,471		4,393
Thereafter		129,386		27,119
Totals	$	321,024	$	53,227