Real Estate Intangibles

6 Months Ended

Jun. 30, 2015

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):


		June 30, 2015		December 31, 2014
Assets:
	In place lease intangibles	$	1,049,407	$	988,290
	Above market tenant leases		82,298		65,684
	Below market ground leases		61,159		62,426
	Lease commissions		21,764		19,536
	Gross historical cost		1,214,628		1,135,936
	Accumulated amortization		(814,084)		(776,501)
	Net book value	$	400,544	$	359,435

	Weighted-average amortization period in years		16.2		17.8

Liabilities:
	Below market tenant leases	$	89,909	$	91,168
	Above market ground leases		7,860		7,859
	Gross historical cost		97,769		99,027
	Accumulated amortization		(42,940)		(40,891)
	Net book value	$	54,829	$	58,136

	Weighted-average amortization period in years		15.5		14.5

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


	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2015		2014		2015		2014
Rental income related to above/below market tenant leases, net	$	(424)	$	290	$	(217)	$	245
Property operating expenses related to above/below market ground leases, net		(334)		(299)		(653)		(610)
Depreciation and amortization related to in place lease intangibles and lease commissions		(31,973)		(59,603)		(56,297)		(138,996)

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


		Assets		Liabilities
2015	$	58,072	$	$3,364
2016		72,338		6,512
2017		43,880		6,052
2018		29,943		5,583
2019		23,946		5,325
Thereafter		172,365		27,993
Total	$	400,544	$	54,829