	Years ended December 31,
	2018			2017
Cost
Balance, beginning of year	$	1,534,599,000		$	1,496,429,000
Properties transferred to held for sale		(61,505,000	)		(15,971,000	)
Property acquisitions		6,481,000			30,997,000
Property dispositions		—			(4,332,000	)
Write-off fully-depreciated assets		—			(2,276,000	)
Improvements and betterments		29,107,000			29,752,000
Balance, end of the year	$	1,508,682,000		$	1,534,599,000

Accumulated depreciation
Balance, beginning of the year	$	341,943,000		$	313,070,000
Properties transferred held for sale		(14,886,000	)		(4,131,000	)
Property dispositions		—			(1,048,000	)
Write-off fully-depreciated assets		—			(2,276,000	)
Depreciation expense		34,912,000			36,328,000
Balance, end of the year	$	361,969,000		$	341,943,000

Net book value	$	1,146,713,000		$	1,192,656,000

At December 31, 2018, Franklin Village Plaza was pledged as collateral for a mortgage loan payable. See Note 8 - “Mortgage Loans Payable and Credit Facilities”.

On August 8, 2018, the Company purchased a land parcel adjacent to its Riverview Plaza property, located in Philadelphia, Pennsylvania. The purchase price for the land parcel was $1.0 million, which was comprised of $25,000 in cash and approximately 208,000 OP Units (based on the market price of the Company’s common stock).

On August 21, 2018, the Company entered into a deed of lease for Senator Square, a shopping center located in Washington, D.C. The deed of lease conveys fee title in the buildings to the Company and contains future options to acquire fee title in the land at its then fair-value. The purchase price has been allocated to real estate assets and liabilities. This lease is presented in the Company’s financial statements as two separate components as follows: (1) a $5.7 million capital lease obligation for the fee interest in the buildings, and (2) an operating lease for the land. The capital lease obligation was computed through the date of the Company’s first purchase option, as discussed below, and reflects an interest rate of 5.3%.

The lease initially requires monthly payments of $75,000 through maturity in August 2117 unless the Company exercises one of its options to acquire the land. The first such option will be available between the 25th and 33rd anniversaries of the lease, depending on certain property benchmarks, with additional purchase options every 10 years thereafter during the lease term. The lease also provides for 1.5% annual increases which begin on approximately the 8th anniversary of the lease, depending on the aforementioned property benchmarks. In addition, at the time the Company’s first purchase option becomes available, the lease payments will be adjusted to the greater of then fair-value or the current payment amount. The lease payments are subject to similar adjustments at the 25th and 50th anniversaries of such first purchase option.

The Company has also issued a $3.5 million interest only mortgage note receivable to the lessor of Senator Square, which bears interest at 4.5% per annum. The maturity date of this mortgage note can range from 26.5 years to 34.5 years from the date of issuance, based on the aforementioned property benchmarks.

The purchase price for all acquisitions in 2017 have been allocated to real estate assets and liabilities. The following table details all acquisitions in 2017:

		Date	Purchase
Property	Location	Acquired	Price
Christina Crossing	Wilmington, DE	2/22/2017	$	27,902,000
Parcel adjacent to South Philadelphia Shopping Center	Philadelphia, PA	7/6/2017		3,000,000
			$	30,902,000

		Date	Sales		Gain on
Property	Location	Sold	Price		Sale
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
2017
Outparcel Building adjacent to Camp Hill	Camp Hill, PA	2/1/2017	$	10,650,000	$	7,099,000
Fredericksburg Way	Fredericksburg, VA	12/29/2017		2,200,000		-
			$	12,850,000	$	7,099,000
2016
Liberty Marketplace	Dubois, PA	2/11/2016	$	15,000,000	$	-
Upland Square	Pottstown, PA	11/2/2016		83,250,000		-
			$	98,250,000	$	-

The Company recorded impairment charges $9.4 million during 2018 relating to West Bridgewater Plaza, $9.5 million during 2017 relating to Fredericksburg Way, and $6.3 million during 2016 relating to Upland Square, which are included in continuing operations in the accompanying consolidated statements of operations.

As of December 31, 2018, Carll’s Corner, located in Bridgeton, New Jersey, and Maxatawny Marketplace, located in Maxatawny, Pennsylvania, have been classified as “real estate held for sale” on the accompanying consolidated balance sheet. The

Company recorded impairment charges of $11.3 million in connection with these properties during 2018.