IDENTIFIED INTANGIBLE ASSETS AND LIABILITIES

Our identified intangible assets (acquired in-place and above and below-market leases) and liabilities (acquired below-market leases), net of accumulated amortization were $76.3 million and $168.5 million as of June 30, 2018, respectively, and $87.2 million and $181.0 million as of December 31, 2017, respectively.

Amortization of acquired below-market leases, net of acquired above-market leases resulted in additional rental income of $7.8 million and $10.5 million for the three and six months ended June 30, 2018, respectively, and $2.1 million and $4.1 million for the same periods in 2017.

Amortization of acquired in-place leases and customer relationships resulted in additional depreciation and amortization expense of $5.8 million and $8.6 million for the three and six months ended June 30, 2018 and $2.1 million and $3.1 million for the same periods in 2017.

Certain shopping centers are subject to ground leases or ground and building leases. Amortization of these acquired below-market leases resulted in additional rent expense of $0.3 million and $0.5 million for the three and six months ended June 30, 2018 and $0.1 million and $0.5 million for the same periods in 2017.

The following table sets forth the estimated annual amortization expense related to intangible assets and liabilities for the five succeeding years commencing January 1, 2019:



(Amounts in thousands)	Below-Market		Above-Market				Below-Market
Year	Operating Lease Income		Operating Lease Expense		In-Place Leases		Ground Leases
2019	$	11,201	$	1,293	$	7,972	$	972
2020	11,034		1,016		6,698		972
2021	10,843		794		5,398		622
2022	10,500		426		4,104		590
2023	10,238		327		3,731		590