Intangibles

The following table summarizes the Company’s intangible lease assets (in thousands):



	December 31,
Intangible lease assets	2018			2017
Gross intangible lease assets	$	556,114		$	795,305
Accumulated depreciation and amortization	(251,035		)	(385,223		)
Net intangible lease assets	$	305,079		$	410,082

The following table summarizes the Company’s intangible lease liabilities (in thousands):



	December 31,
Intangible lease liabilities	2018			2017
Gross intangible lease liabilities	$	94,444		$	126,212
Accumulated depreciation and amortization	(39,781		)	(73,633		)
Net intangible lease liabilities	$	54,663		$	52,579

The following table sets forth amortization related to deferred leasing costs and acquisition-related intangibles (in thousands):



	Year Ended December 31,
	2018		2017		2016
Depreciation and amortization expense related to amortization of lease-up intangibles	$	67,350	$	76,732	$	84,487
Rental and related revenues related to amortization of net below market lease liabilities	5,253		2,030		3,877
Operating expense related to amortization of net below market ground lease intangibles	636		740		664

The following table summarizes the estimated annual amortization for each of the five succeeding fiscal years and thereafter (in thousands):



	Rental and Related Revenues⁽¹⁾		Operating Expense⁽²⁾		Depreciation and Amortization⁽³⁾
2019	$	4,399	$	505	$	50,762
2020	3,670		621		39,433
2021	3,587		738		32,214
2022	4,331		738		26,438
2023	4,269		738		24,293
Thereafter	16,521		29,901		80,812
	$	36,777	$	33,241	$	253,952

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(1)	The amortization of net below market lease intangibles is recorded as an increase to rental and related income.


(2)	The amortization of net below market ground lease intangibles is recorded as an increase to operating expense.


(3)	The amortization of lease-up intangibles is recorded to depreciation and amortization expense.