	Years ended December 31,
	2020			2019
Cost
Balance, beginning of year	$	1,515,206,000		$	1,508,682,000
Properties transferred to held for sale		(22,512,000	)		(36,265,000	)
Property acquisitions		—			9,333,000
Outparcel dispositions		(840,000	)		—
Asset write-offs		—			(3,633,000	)
Improvements and betterments		35,624,000			37,089,000
Balance, end of the year	$	1,527,478,000		$	1,515,206,000

Accumulated depreciation
Balance, beginning of the year	$	389,861,000		$	361,969,000
Properties transferred held for sale		(3,947,000	)		(10,143,000	)
Outparcel dispositions		(90,000	)		—
Asset write-offs		—			(3,107,000	)
Depreciation expense		42,745,000			41,142,000
Balance, end of the year	$	428,569,000		$	389,861,000

Net book value	$	1,098,909,000		$	1,125,345,000

At December 31, 2020, Franklin Village Plaza was pledged as collateral for a mortgage loan payable. See Note 8 - “Mortgage Loans Payable and Credit Facilities”.

On June 19, 2019, the Company purchased Girard Plaza, a shopping center adjacent to its South Philadelphia property, located in Philadelphia, Pennsylvania. The purchase price for the property was $8.5 million, which has been allocated to real estate assets and liabilities.

		Date	Sales		Gain on
Property	Location	Sold	Price		Sale
2020
Metro Square	Owings Mills, MD	7/9/2020	$	4,288,000	$	-
Oakland Mills outparcel building	Columbia, MD	9/17/2020		1,050,000		643,000
Glen Allen Shopping Center	Glen Allen, VA	10/8/2020		8,540,000		1,780,000
Pine Grove Plaza outparcel building	Brown Mills, NJ	11/2/2020		1,100,000		565,000
Suffolk Plaza	Suffolk, VA	12/10/2020		6,950,000		1,408,000
			$	21,928,000	$	4,396,000
2019
Maxatawny Marketplace	Maxatawny, PA	2/15/2019	$	10,330,000	$	101,000
Fort Washington Center	Fort Washington, PA	6/26/2019		9,048,000		2,841,000
			$	19,378,000	$	2,942,000
2018
Mechanicsburg Center	Mechanicsburg, PA	8/28/2018	$	16,100,000	$	4,864,000
West Bridgewater Plaza	West Bridgewater, MA	9/28/2018		3,500,000		-
			$	19,600,000	$	4,864,000

The Company recorded impairment charges of $7.2 million relating to Metro Square during 2020, and $9.4 million relating to West Bridgewater Plaza during 2018, which are included in continuing operations in the accompanying consolidated statements of operations.

As of December 31, 2020, Carll’s Corner, located in Bridgeton, New Jersey, and The Commons, located in Dubois Pennsylvania, have been classified as “real estate held for sale” on the accompanying consolidated balance sheet.

During, 2020, the Company recorded impairment charges of $0.4 million in connection with The Commons. In addition, the Company recorded an impairment charge of $8.9 million in connection with The Commons in 2019 and $11.3 million in connection with Carll’s Corner in 2018. These impairment charges have been included in continuing operations in the accompanying consolidated statement of operations.

On July 23, 2020, the Company entered into a commercial lease agreement (the “Lease”) with the Government of the District of Columbia (the “District”), for the lease by the District of office space in a new six-story building to be constructed by the Company at Senator Square. The building is planned to house the new office headquarters for the District of Columbia’s Department of General Services’ (“DGS”) 700-member workforce. The term of the Lease is 20 years and 10 months, to commence upon substantial completion and delivery to DGS. The Company anticipates commencement of construction to occur in the first quarter of 2021 and currently estimates that the space will be delivered during the end of the fourth quarter 2022.

Upon completion of the building, the District will be obligated to pay initial annual net rent of approximately $5.4 million per year, subject to a 2.5% annual escalator on each anniversary of rent commencement, plus certain operating costs, property taxes and amortization of tenant improvements together totaling approximately an additional $8.1 million per year, for an aggregate total annual rent of approximately $13.5 million. The Lease provides for a free rent period of 10 months immediately following rent commencement. The Lease also provides the District with a tenant credit of approximately $6.8 million to be applied, at the District’s election, against either annual rent or any other tenant payment obligations including tenant improvement costs, in excess of the tenant improvement allowance. Pursuant to the Lease, the landlord will contribute up to $155 per rentable square foot toward the cost of tenant improvements, to be amortized over 240 months. In addition, the Lease provides that the Company will contribute $9.38 per rentable square foot in

additional tenant improvement allowance between the 10th and 12th Lease years, upon the District’s timely election. The obligations of the District under the Lease are subject to annual budget appropriation.