Property

Our property consists of the following (in thousands):



	December 31,
	2017		2016
Land	$	1,068,022	$	1,107,072
Land held for development	69,205		82,953
Land under development	48,985		51,761
Buildings and improvements	3,232,074		3,489,685
Construction in-progress	80,573		57,674
Total	$	4,498,859	$	4,789,145

During the year ended December 31, 2017, we sold 18 centers and other property. Aggregate gross sales proceeds from these transactions approximated $446.6 million and generated gains of approximately $218.6 million. Also, for the year ended December 31, 2017, we invested $57.2 million in new development projects, which includes the purchase of the retail portion of a mixed-use project in Seattle, Washington that was subject to a contractual obligation at December 31, 2016.

At December 31, 2017, three centers, totaling $78.7 million before accumulated depreciation, were classified as held for sale. At December 31, 2016, one center, totaling $1.6 million before accumulated depreciation, was classified as held for sale. None of these centers qualified to be reported in discontinued operations, and all but one have been sold subsequent to the end of the applicable reporting period.