Real Estate Intangibles

6 Months Ended

Jun. 30, 2017

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, 2017		December 31, 2016
Assets:
	In place lease intangibles	$	1,278,755	$	1,252,143
	Above market tenant leases		64,408		61,700
	Below market ground leases		62,224		61,628
	Lease commissions		30,654		27,413
	Gross historical cost		1,436,041		1,402,884
	Accumulated amortization		(1,053,353)		(966,714)
	Net book value	$	382,688	$	436,170

	Weighted-average amortization period in years		15.1		13.7

Liabilities:
	Below market tenant leases	$	90,683	$	89,468
	Above market ground leases		8,540		8,107
	Gross historical cost		99,223		97,575
	Accumulated amortization		(55,749)		(52,134)
	Net book value	$	43,474	$	45,441

	Weighted-average amortization period in years		15.4		15.2

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,
	2017		2016		2017		2016
Rental income related to above/below market tenant leases, net	$	267	$	210	$	571	$	290
Property operating expenses related to above/below market ground leases, net		(307)		(311)		(619)		(622)
Depreciation and amortization related to in place lease intangibles and lease commissions		(35,439)		(31,109)		(74,741)		(65,473)

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

		Assets		Liabilities
2017	$	71,356	$	3,337
2018		83,762		6,190
2019		35,095		5,731
2020		24,793		5,234
2021		20,695		4,746
Thereafter		146,987		18,236
Total	$	382,688	$	43,474