Real Estate Intangibles

12 Months Ended

Dec. 31, 2019

Intangible Assets, Net (Excluding Goodwill) [Abstract]

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, 2019			December 31, 2018
Assets:
In place lease intangibles	$	1,513,836		$	1,410,725
Above market tenant leases	59,540			63,935
Below market ground leases⁽¹⁾	—			64,513
Lease commissions	43,675			41,986
Gross historical cost	1,617,051			1,581,159
Accumulated amortization	(1,181,158		)	(1,197,336		)
Net book value	$	435,893		$	383,823

Weighted-average amortization period in years	10.3			16.0

Liabilities:
Below market tenant leases	$	99,035		$	81,676
Above market ground leases⁽¹⁾	—			8,540
Gross historical cost	99,035			90,216
Accumulated amortization	(49,390		)	(44,266		)
Net book value	$	49,645		$	45,950

Weighted-average amortization period in years	8.6			14.7

⁽¹⁾ Effective on January 1, 2019 with the adoption of ASC 842, above and below market ground lease intangibles are reported within the right of use assets, net line on the Consolidated Balance Sheet.

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



	Year Ended December 31,
	2019			2018			2017
Rental income related to (above)/below market tenant leases, net	$	508		$	(1,269	)	$	875
Depreciation and amortization related to in place lease intangibles and lease commissions	(135,047		)	(122,515		)	(145,132		)

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



	Assets		Liabilities
2020	$	119,973	$	9,498
2021	59,824		8,529
2022	40,802		7,758
2023	34,803		5,483
2024	27,415		3,362
Thereafter	153,076		15,015
Totals	$	435,893	$	49,645