Real Estate Intangibles

12 Months Ended

Dec. 31, 2012

Real Estate Intangibles [Abstract]

Real Estate Intangibles

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):

		December 31, 2012		December 31, 2011
Assets:
	In place lease intangibles	$	541,729	$	332,645
	Above market tenant leases		56,086		35,973
	Below market ground leases		61,450		51,316
	Lease commissions		14,419		8,265
	Gross historical cost		673,684		428,199
	Accumulated amortization		(257,242)		(148,380)
	Net book value	$	416,442	$	279,819
	Weighted-average amortization period in years		16.4		17.0
Liabilities:
	Below market tenant leases	$	77,036	$	67,284
	Above market ground leases		9,490		5,020
	Gross historical cost		86,526		72,304
	Accumulated amortization		(27,753)		(21,387)
	Net book value	$	58,773	$	50,917
	Weighted-average amortization period in years		14.3		12.3

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

	Year Ended December 31,
	2012		2011		2010
Rental income related to above/below market tenant leases, net	$	1,120	$	3,340	$	3,829
Property operating expenses related to above/below market ground leases, net		(1,285)		(1,161)		(1,049)
Depreciation and amortization related to in place lease intangibles and lease commissions		(103,044)		(98,856)		(18,298)

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

		Assets		Liabilities
2013	$	112,730	$	7,200
2014		62,787		6,616
2015		29,220		5,645
2016		23,201		5,233
2017		23,453		4,920
Thereafter		165,051		29,159
Totals	$	416,442	$	58,773