Real Estate Intangibles

12 Months Ended

Dec. 31, 2014

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, 2014		December 31, 2013
Assets:
	In place lease intangibles	$	988,290	$	937,357
	Above market tenant leases		65,684		55,939
	Below market ground leases		62,426		59,165
	Lease commissions		19,536		18,293
	Gross historical cost		1,135,936		1,070,754
	Accumulated amortization		(776,501)		(571,008)
	Net book value	$	359,435	$	499,746

	Weighted-average amortization period in years		17.7		16.7

Liabilities:
	Below market tenant leases	$	91,168	$	76,381
	Above market ground leases		7,859		9,490
	Gross historical cost		99,027		85,871
	Accumulated amortization		(40,891)		(34,434)
	Net book value	$	58,136	$	51,437

	Weighted-average amortization period in years		14.4		14.3

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


	Year Ended December 31,
	2014		2013		2012
Rental income related to above/below market tenant leases, net	$	509	$	748	$	1,120
Property operating expenses related to above/below market ground leases, net		(1,248)		(1,208)		(1,285)
Depreciation and amortization related to in place lease intangibles and lease commissions		(214,966)		(246,938)		(103,044)

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


		Assets		Liabilities
2015	$	58,224	$	3,278
2016		56,656		9,513
2017		54,241		10,795
2018		53,715		7,758
2019		23,038		6,474
Thereafter		113,561		20,318
Totals	$	359,435	$	58,136