Our consolidated investments in real estate, including real estate assets held for sale as described in Note 19 – “Assets Classified as Held for Sale” to our consolidated financial statements, consisted of the following as of December 31, 2019 and 2018 (in thousands):



	December 31,
	2019			2018
Rental properties:
Land (related to rental properties)	$	2,225,785		$	1,625,349
Buildings and building improvements	11,775,132			9,986,635
Other improvements	1,277,862			976,627
Rental properties	15,278,779			12,588,611
Development and redevelopment of new Class A properties:
Development and redevelopment projects	2,057,084			1,460,814
Future development projects	182,746			98,802
Gross investments in real estate	17,518,609			14,148,227
Less: accumulated depreciation	(2,704,657		)	(2,263,797		)
Net investments in real estate – North America	14,813,952			11,884,430
Net investments in real estate – Asia	30,086			29,263
Investments in real estate	$	14,844,038		$	11,913,693



		Square Footage
Market	Number of Properties	Future Development	Active Redevelopment	Operating With Future Development/Redevelopment	Operating	Purchase Price
Greater Boston	12	668,000	153,157	154,855	615,439	$	858,600
San Francisco	8	—	347,912	478,000	247,770	735,450
New York City	—	135,938	—	—	—	25,000
San Diego	16	869,000	—	93,220	912,419	474,214		⁽¹⁾
Seattle	1	188,400	—	18,680	—	28,500
Maryland	3	435,000	—	—	138,938	76,130
Other	7	54,000	—	134,678	34,534	77,000
Year ended December 31, 2019	47	2,350,338	501,069	879,433	1,949,100	$	2,274,894

We evaluated each acquisition to determine whether the integrated set of assets and activities acquired met the definition of a business. Acquisitions that do not meet the definition of a business are accounted for as asset acquisitions. An integrated set of assets and activities does not qualify as a business if substantially all of the fair value of the gross assets is concentrated in either a single identifiable asset or a group of similar identifiable assets, or if the acquired assets do not include a substantive process.

Based upon our evaluation of each acquisition, we determined that substantially all of the fair value related to each acquisition is concentrated in a single identifiable asset or a group of similar identifiable assets, or is associated with a land parcel with no operations. Accordingly, each transaction did not meet the definition of a business and consequently was accounted for as an asset acquisition. In each of these transactions, we allocated the total consideration for each acquisition to the individual assets and liabilities acquired on a relative fair value basis.

During the year ended December 31, 2019, we acquired 47 properties for an aggregate purchase price of $2.3 billion. In connection with our acquisitions, we recorded in-place leases aggregating $197.8 million and below-market leases in which we are the lessor aggregating $90.2 million. As of December 31, 2019, the weighted-average amortization period remaining on our acquired in-place and below-market leases related to properties acquired in 2019 was 9.0 years and 11.9 years, respectively, and 9.9 years in total.

The balances of acquired below-market tenant leases, and related accumulated amortization, classified in accounts payable, accrued expenses, and other liabilities in our consolidated balance sheets as of December 31, 2019 and 2018, were as follows (in thousands):

For the years ended December 31, 2019, 2018, and 2017, we recognized in rental revenues approximately $30.3 million, $22.3 million, and $19.3 million, respectively, related to the amortization of acquired below-market leases.

The amounts in the table above excludes the balances of acquired below-market ground leases, and related accumulated amortization, classified in other assets in our consolidated balance sheets as of December 31, 2019 and 2018. Refer to Note 8 – “Other Assets” to our consolidated financial statements.

The weighted-average amortization period of the value of acquired below-market leases was approximately 5.1 years, and the estimated annual amortization of the value of acquired below-market leases as of December 31, 2019, is as follows (in thousands):

The balances of acquired in-place leases, and related accumulated amortization, are classified in other assets in our consolidated balance sheets. As of December 31, 2019 and 2018, these amounts were as follows (in thousands):

Amortization for these intangible assets, classified in depreciation and amortization expense in our consolidated statements of operations, was approximately $49.1 million, $34.3 million, and $19.6 million for the years ended December 31, 2019, 2018, and 2017, respectively. The weighted-average amortization period of the value of acquired in-place leases was approximately 5.9 years, and the estimated annual amortization of the value of acquired in-place leases as of December 31, 2019, is as follows (in thousands):

For the discussion of our sales of partial interests in 75/125 Binney Street, 5200 Illumina Way, and 500 Forbes Boulevard in 2019 and the formation of consolidated joint ventures that own these properties, refer to “Sales of Partial Interests and Formation of Consolidated Joint Ventures in 2019” section within Note 4 – “Consolidated and Unconsolidated Real Estate Joint Ventures” to our consolidated financial statements.

During the three months ended June 30, 2019, we classified as held for sale 6138/6150 Nancy Ridge Drive aggregating 56,698 RSF, located in our Sorrento Mesa submarket. In December 2019, we completed the sale of the property for a sales price of $6.6 million, or $117 per RSF, and recognized a gain of $474 thousand.

In December 2019, we decided to sell two of our real estate assets aggregating 123,862 RSF located in non-cluster markets to allow for reinvestment of this capital into our highly leased value-creation pipeline. We evaluated these assets under the held for sale impairment model and determined that these investments met the criteria for classification as held for sale but did not meet the criteria for classification as discontinued operations in our consolidated financial statements. Upon classification as held for sale, we recognized impairment charges aggregating $12.3 million to lower the carrying amounts to their respective estimated fair value less cost to sell. For additional information, refer to Note 19 – “Assets Classified as Held for Sale” to our consolidated financial statements.