Property, net:

Property at December 31, 2017 and 2016 consists of the following:



	2017			2016
Land	$	1,567,152		$	1,607,590
Buildings and improvements	6,385,035			6,511,741
Tenant improvements	620,352			622,878
Equipment and furnishings	187,998			177,036
Construction in progress	366,996			289,966
	9,127,533			9,209,211
Less accumulated depreciation	(2,018,303		)	(1,851,901		)
	$	7,109,230		$	7,357,310

Depreciation expense for the years ended December 31, 2017, 2016 and 2015 was $277,917, $277,270 and $354,977, respectively.

The gain on sale or write down of assets, net for the year ended December 31, 2017 includes a gain of $59,577 on the sale of Cascade Mall and Northgate Mall (See Note 15—Dispositions), $14,597 on the sale of 500 North Michigan Avenue (See Note 15—Dispositions) and $1,564 on the sales of land. These gains were offset in part by a loss of $22,108 on impairment, $10,138 on the write down of an investment in non-real estate assets and $1,046 on the write off of development costs. The loss on impairment was due to the reduction of the estimated holding periods of Southridge Center and Promenade at Casa Grande.

The gain on sale or write down of assets, net for the year ended December 31, 2016 includes a gain of $101,629 on the sale of a 40% ownership interest in Arrowhead Towne Center (See Note 4—Investments in Unconsolidated Joint Ventures), $340,734 on the sale of a 49% ownership interest in the MAC Heitman Portfolio (See Note 4—Investments in Unconsolidated Joint Ventures), $24,894 on the sale of Capitola Mall (See Note 15—Dispositions) and $4,546 on the sale of land. These gains were offset in part by a loss of $39,671 on impairment, a charge of $12,180 from a contingent consideration obligation, a loss of $3,066 on the sale of a former Mervyn's store (See Note 15—Dispositions) and $1,538 on the write-off of development costs. The loss on impairment was due to the reduction of the estimated holding periods of Cascade Mall, Promenade at Casa Grande, The Marketplace at Flagstaff and a freestanding store.

The gain on sale or write down of assets, net for the year ended December 31, 2015 includes the gain of $311,194 on the sale of a 40% ownership interest in the PPR Portfolio (See Note 4—Investments in Unconsolidated Joint Ventures), $73,726 on the sale of Panorama Mall (See Note 15—Dispositions), $2,336 on the sale of assets and $1,807 on the sale of land offset in part by a loss of $9,963 on impairment and $852 on the write-off of development costs. The loss on impairment was due to the reduction of the estimated holding periods of Flagstaff Mall (See Note 15—Dispositions) and a freestanding store.

The following table summarizes certain of the Company's assets that were measured on a nonrecurring basis as a result of impairment charges recorded for the years ended December 31, 2017, 2016 and 2015 as described above:



Years ended December, 31	Total Fair Value Measurement		Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
Years ended December, 31	Total Fair Value Measurement		(Level 1)		(Level 2)		(Level 3)
2017	$	38,000	$	—	$	38,000	$	—
2016	$	86,100	$	—	$	—	$	86,100
2015	$	49,700	$	—	$	6,200	$	43,500

The fair value relating to impairments that were based on sales contracts were classified within Level 2 of the fair value hierarchy. The fair value relating to impairment assessments that were not based on sales contracts were based on a discounted cash flow model that included all cash inflows and outflows over a specific holding period. Such projected cash flows are comprised of contractual rental revenues and forecasted rental revenues and expenses based upon market conditions and expectations for growth. Terminal capitalization rates and discount rates utilized in these models are based on a reasonable range of current market rates for each property analyzed. Based upon these inputs, the Company determined that its valuations of properties using a discounted cash flow model are classified within Level 3 of the fair value hierarchy.

The following table sets forth quantitative information about the unobservable inputs of the Company’s Level 3 real estate recorded as of December 31, 2016 and 2015:



Unobservable Inputs	2016	2015
Terminal capitalization rate	7.0% - 10.0%	9.0%
Discount rate	8.0% - 15.0%	9.5%
Market rents per square foot	$2.00 - $20.00	$5.00 - $150.00