Our consolidated investments in real estate, including real estate assets held for sale as described in Note 18 – “Assets classified as held for sale” to our consolidated financial statements, consisted of the following as of December 31, 2021 and 2020 (in thousands):


	December 31,
	2021		2020
Rental properties:
Land (related to rental properties)	$	3,782,182	$	2,550,571
Buildings and building improvements	16,312,402		13,364,561
Other improvements	2,109,884		1,508,776
Rental properties	22,204,468		17,423,908
Development and redevelopment of new Class A properties:
Development and redevelopment projects	5,054,632		3,075,453
Future development projects	1,474,008		738,994
Gross investments in real estate	28,733,108		21,238,355
Less: accumulated depreciation	(3,766,758)		(3,178,024)
Net investments in real estate – North America	24,966,350		18,060,331
Net investments in real estate – Asia	14,319		32,041
Investments in real estate	$	24,980,669	$	18,092,372


		Square Footage
Market	Number of Properties	Future Development	Active Development/ Redevelopment	Operating With Future Development/Redevelopment	Operating	Purchase Price
Greater Boston	10	1,870,992	1,497,877	745,209	936,455	$	2,817,748
San Francisco Bay Area	10	1,530,830	—	595,503	—	709,050
San Diego	19	951,235	—	927,334	413,909	519,710
Maryland	5	258,000	94,256	—	595,381	80,382
Research Triangle	—	1,055,000	—	—	—	91,000
Other	43	4,999,768	390,675	1,229,735	1,286,123	1,251,264
Year ended December 31, 2021	87	10,665,825	1,982,808	3,497,781	3,231,868	$	5,469,154	(1)

(1)Represents the aggregate contractual purchase price of our acquisitions, which differ from purchases of real estate in our consolidated statements of cash flows due to the timing of payment, closing costs, and other acquisition adjustments such as prorations of rents and expenses.

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 therefore was accounted for as an asset acquisition. In each of these transactions, we allocated the total consideration for each acquisition to the individual tangible and intangible assets and liabilities acquired on a relative fair value basis.

During the year ended December 31, 2021, we acquired 87 properties for an aggregate purchase price of $5.5 billion. In connection with our acquisitions, we recorded in-place lease assets aggregating $306.9 million and below-market lease liabilities in which we are the lessor aggregating $120.2 million. As of December 31, 2021, the weighted-average amortization period remaining on our in-place leases and below-market leases acquired during the year ended December 31, 2021 was 8.8 years and 9.7 years, respectively, and 9.1 years in aggregate.

In January 2022, we completed acquisitions in our key life science cluster submarkets aggregating 4.5 million SF, comprising 4.1 million RSF of future development and redevelopment opportunities and 381,760 RSF of operating space, for an aggregate purchase price of $1.2 billion.

For the discussion of the formation of our consolidated real estate joint venture, refer to the “Formation of consolidated real estate joint ventures and sales of partial interest” section in Note 4 – “Consolidated and unconsolidated real estate joint ventures” to our consolidated financial statements.

As of December 31, 2020, we had a 56.8% interest in an unconsolidated real estate joint venture that owned an operating property aggregating 80,032 RSF located at 704 Quince Orchard Road in our Gaithersburg submarket of Maryland. We accounted for this joint venture under the equity method of accounting. On March 25, 2021, we acquired the remaining 43.2% interest in this real estate joint venture for $9.4 million and fully repaid the outstanding secured loan with principal and accrued interest aggregating $14.6 million as of March 25, 2021.

As a result of this acquisition, we now own 100% of this property and consolidate its results in our consolidated financial statements. The acquired property did not meet the definition of a business and the transaction was accounted for as an asset acquisition. Under our existing accounting policy election, we follow the asset acquisition cost accumulation and allocation model. Accordingly, we did not remeasure our previously held equity interest at fair value and did not recognize a gain or loss in our consolidated statements of operations. The acquisition consideration and the carrying amount of our existing equity interest were allocated to the individual assets acquired and liabilities assumed on a relative fair value basis.

Refer to Note 2 – “Summary of significant accounting policies” to our consolidated financial statements for more information about our evaluation of applicability of accounting guidance on asset acquisitions or business combinations.

The balances of acquired below-market tenant leases existing as of December 31, 2021 and 2020, and related accumulated amortization, classified in accounts payable, accrued expenses, and other liabilities in our consolidated balance sheets as of December 31, 2021 and 2020 were as follows (in thousands):

For the years ended December 31, 2021, 2020, and 2019, we recognized in rental revenues approximately $57.7 million, $57.8 million, and $30.3 million, respectively, related to the amortization of acquired below-market leases existing as of the end of each respective year.

The weighted-average amortization period of the value of acquired below-market leases existing as of December 31, 2021 was approximately 5.4 years, and the estimated annual amortization of the value of acquired below-market leases as of December 31, 2021 is as follows (in thousands):

The balances of acquired in-place leases, and related accumulated amortization, classified in other assets in our consolidated balance sheets as of December 31, 2021 and 2020 were as follows (in thousands):

Amortization for these intangible assets, classified in depreciation and amortization expense in our consolidated statements of operations, was approximately $146.6 million, $105.4 million, and $49.1 million for the years ended December 31, 2021, 2020, and 2019, respectively. The weighted-average amortization period of the value of acquired in-place leases was approximately 8.3 years, and the estimated annual amortization of the value of acquired in-place leases as of December 31, 2021 is as follows (in thousands):

During the three months ended September 30, 2021, we completed the sales of three office properties located in our San Francisco Bay Area and Seattle markets for an aggregate purchase price of $73.1 million and recognized a loss on sales of real estate aggregating $435 thousand.

In December 2021, we completed the sale of our 2301 5th Avenue property aggregating 197,135 RSF, located in our Lake Union submarket of Seattle, for a sales price of $118.7 million, or $602 per RSF, and recognized a gain on sale of real estate of $23.2 million.

In December 2021, we competed the sale of our entire 49.0% interest in the Menlo Gateway unconsolidated real estate joint venture, located in our Greater Stanford submarket of San Francisco Bay Area. We sold our interest for a contractual price of $397.9 million which consisted of sales price of $541.5 million less our share of debt held by the unconsolidated real estate joint venture assumed by the buyer, aggregating $143.6 million. In connection with the sale, we recognized a gain of $101.1 million, which is classified within gain on sales of real estate within our consolidated statements of operations for the year ended December 31, 2021.

The aforementioned gains and losses were classified in gain on sales of real estate within our consolidated statements of operations for the year ended December 31, 2021. For the discussion of our sales of partial interests completed during the year ended December 31, 2021, refer to the “Formation of consolidated real estate joint ventures and sales of partial interest” and “Unconsolidated real estate joint ventures” sections within Note 4 – “Consolidated and unconsolidated real estate joint ventures” to our consolidated financial statements.

During the year ended December 31, 2021, we recognized real estate asset impairments of office-related properties aggregating $52.7 million, primarily consisting of the following:

•Impairment charge of $22.5 million during the three months ended September 30, 2021, upon classification as held for sale of an option to purchase a land parcel in our SoMa submarket for the development of an office property, to reduce the option’s carrying amount to its estimated fair value less costs to sell. We completed the sale of the option during the three months ended December 31, 2021, at no gain or loss.

•Impairment charge of $18.6 million during the three months ended September 30, 2021, to reduce the carrying amount of a property located in a non-core submarket to its estimated fair value less costs to sell, upon our review of the current local market conditions.

•Impairment charges aggregating $6.9 million during the six months ended June 30, 2021, to reduce the carrying amounts of three office properties located in our San Francisco Bay Area and Seattle markets to their estimated fair values less costs to sell, based on the sales price negotiated for each property during this period. We completed the sales of these properties during the three months ended September 30, 2021.

Refer to the “Impairment of long-lived assets” section within Note 2 – “Summary of significant accounting policies” to our consolidated financial statements for additional information.