7.Intangible Assets and Liabilities

The following summarizes our intangible assets (primarily acquired above-market leases and acquired in-place leases) and intangible liabilities (primarily acquired below-market leases) as of September 30, 2016 and December 31, 2015.

	As of
(Amounts in thousands)	September 30, 2016			December 31, 2015
Intangible assets:
Gross amount	$	567,142		$	655,194
Accumulated amortization		(160,956	)		(143,987	)
	$	406,186		$	511,207
Intangible liabilities:
Gross amount	$	199,416		$	221,672
Accumulated amortization		(55,219	)		(41,931	)
	$	144,197		$	179,741

Amortization of acquired below-market leases, net of acquired above-market leases, resulted in an increase to rental income of $3,112,000 and $1,477,000 for the three months ended September 30, 2016 and 2015, respectively, and $6,593,000 and $3,239,000 for the nine months ended September 30, 2016 and 2015, respectively. The three and nine months ended September 30, 2016 include $2,485,000 and $10,315,000 of income, respectively, from the accelerated amortization of a below-market lease liability in connection with a tenant’s lease modification and $1,743,000 and $11,577,000 of expense, respectively, from the write-off above-market lease assets in connection with lease terminations. Estimated annual amortization of acquired below-market leases, net of acquired above-market leases, for each of the five succeeding years commencing January 1, 2017 is as follows.

(Amounts in thousands)
2017	$	9,416
2018		10,054
2019		9,372
2020		7,929
2021		3,548

Amortization of acquired in-place leases (a component of depreciation and amortization expense) was $21,917,000 and $29,376,000 for the three months ended September 30, 2016 and 2015, respectively and $76,072,000 and $100,006,000 for the nine months ended September 30, 2016 and 2015, respectively. Estimated annual amortization of acquired in-place leases for each of the five succeeding years commencing January 1, 2017 is as follows.

(Amounts in thousands)
2017	$	54,057
2018		48,366
2019		43,754
2020		38,335
2021		26,355