Real Estate Intangibles

12 Months Ended

Dec. 31, 2016

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, 2016		December 31, 2015
Assets:
	In place lease intangibles	$	1,252,143	$	1,179,537
	Above market tenant leases		61,700		67,529
	Below market ground leases		61,628		80,224
	Lease commissions		27,413		23,295
	Gross historical cost		1,402,884		1,350,585
	Accumulated amortization		(966,714)		(881,096)
	Net book value	$	436,170	$	469,489

	Weighted-average amortization period in years		13.7		13.4

Liabilities:
	Below market tenant leases	$	89,468	$	93,089
	Above market ground leases		8,107		7,907
	Gross historical cost		97,575		100,996
	Accumulated amortization		(52,134)		(46,048)
	Net book value	$	45,441	$	54,948

	Weighted-average amortization period in years		15.2		14.5

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


	Year Ended December 31,
	2016		2015		2014
Rental income related to above/below market tenant leases, net	$	919	$	(2,746)	$	509
Property operating expenses related to above/below market ground leases, net		(1,241)		(1,272)		(1,248)
Depreciation and amortization related to in place lease intangibles and lease commissions		(132,141)		(115,855)		(214,966)

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


		Assets		Liabilities
2017	$	141,094	$	6,544
2018		78,905		5,959
2019		33,228		5,551
2020		22,958		5,074
2021		19,045		4,586
Thereafter		140,940		17,727
Totals	$	436,170	$	45,441