Acquisitions and dispositions for the periods presented were completed in accordance with our strategy to reposition our investment concentration among the markets in which we operate and to increase our overall investments in quality industrial projects. Transaction costs related to asset acquisitions are capitalized and transaction costs related to business combinations and dispositions are expensed.

We acquired ten properties during the year ended December 31, 2020. We determined that these ten properties did not meet the definition of a business and, accordingly, we accounted for them as asset acquisitions as opposed to business combinations.

The following table summarizes amounts recognized for each major class of assets and liabilities (in thousands) for these acquisitions during the year ended December 31, 2020:


Real estate assets	$	410,481
Lease related intangible assets	14,460
Total acquired assets	$	424,941
Secured debt	$	25,455
Below market lease liabilities	14,124

The leases in the acquired properties had a weighted average remaining life at acquisition of approximately 6.4 years.

We acquired six properties during the year ended December 31, 2019. We determined that these six properties did not meet the definition of a business and, accordingly, we accounted for them as asset acquisitions as opposed to business combinations.

The following table summarizes amounts recognized for each major class of assets (in thousands) for these acquisitions during the year ended December 31, 2019:

The leases in the acquired properties had a weighted average remaining life at acquisition of approximately 6.5 years.

We acquired nine properties during the year ended December 31, 2018. We determined that these nine properties did not meet the definition of a business and, accordingly, we accounted for them as asset acquisitions as opposed to business combinations.

The following table summarizes amounts recognized for each major class of asset and liability (in thousands) for these acquisitions during the year ended December 31, 2018:


Real estate assets	$	328,126
Lease related intangible assets	24,996

Total acquired assets	$	353,122
Below market lease liability	$	505

The leases in the acquired properties had a weighted average remaining life at acquisition of approximately 11.3 years.

We determine the fair value of the individual components of real estate asset acquisitions primarily through calculating the "as-if vacant" value of a building, using an income approach, which relies significantly upon internally determined assumptions. We have determined that these estimates primarily rely on Level 3 inputs, which are unobservable inputs based on our own assumptions. The most significant assumptions used in calculating the "as-if vacant" value for acquisition activity during 2020 and 2019, respectively, are as follows:


	2020		2019
	Low	High	Low	High
Exit capitalization rate	3.98%	5.46%	4.23%	5.32%
Net rental rate per square foot	$5.28	$18.11	$5.90	$15.60

Capitalized acquisition costs were insignificant and the fair value of the ten properties acquired during the year ended December 31, 2020 was substantially the same as the cost of acquisition.

Dispositions of buildings (see Note 8 for the number of buildings sold in each year, as well as for their classification between continuing and discontinued operations) and undeveloped land generated net cash proceeds of $336.3 million, $432.7 million and $511.4 million in 2020, 2019 and 2018, respectively.

During 2020, we collected the remaining $110.0 million of principal on our outstanding notes receivable, which was related to the sale of our medical office portfolio during 2017.

In September 2019, we completed the sale of 18 non-strategic industrial properties for $217.5 million in proceeds and recorded a gain on sale of $146.3 million. These properties totaled 4.1 million square feet and were located in primarily Midwest markets.