7.	Intangible Assets and Liabilities

The following table summarizes our intangible assets (acquired above-market leases and acquired in-place leases) and intangible liabilities (acquired below-market leases) as of June 30, 2017 and December 31, 2016.

	As of
(Amounts in thousands)	June 30, 2017			December 31, 2016
Intangible assets:
Gross amount	$	536,610		$	579,066
Accumulated amortization		(173,087	)		(166,841	)
	$	363,523		$	412,225
Intangible liabilities:
Gross amount	$	197,593		$	208,367
Accumulated amortization		(63,845	)		(55,349	)
	$	133,748		$	153,018

Amortization of acquired below-market leases, net of acquired above-market leases, resulted in an increase to rental income of $7,981,000 and $7,100,000 for the three months ended June 30, 2017 and 2016, respectively, and $10,989,000 and $3,481,000 for the six months ended June 30, 2017 and 2016, respectively. The six months ended June 30, 2016 included $9,834,000 of expense, from the write-off of an above-market lease asset in connection with the termination of a tenant’s lease. Estimated annual amortization of acquired below-market leases, net of acquired above-market leases, for each of the five succeeding years commencing January 1, 2018 is as follows.

(Amounts in thousands)
2018	$	12,558
2019		10,775
2020		8,765
2021		4,509
2022		1,144

Amortization of acquired in-place leases (a component of depreciation and amortization expense) was $22,649,000 and $23,463,000 for the three months ended June 30, 2017 and 2016, respectively, and $40,423,000 and $54,155,000 for the six months ended June 30, 2017 and 2016, respectively. Estimated annual amortization of acquired in-place leases for each of the five succeeding years commencing January 1, 2018 is as follows.

(Amounts in thousands)
2018	$	52,556
2019		46,561
2020		39,776
2021		27,645
2022		23,031