Property and Equipment and Assets Held-for-Sale

As of December 31, 2018 and 2017, property and equipment, net and assets held-for-sale consists of the following (in thousands):



	2018			2017			Depreciable Lives
Computer equipment	$	3,189		$	3,061		3 years
Software	11,076			11,062			3 years
Office furniture and equipment	873			2,530			5 to 6 years
Laboratory equipment	18,348			51,315			7 years
Leasehold improvements	23,932			25,356			Shorter of asset life or lease term
Less: accumulated depreciation	(36,474		)	(63,408		)
	$	20,944		$	29,916

Assets held-for-sale	$	1,324		$	—

During 2018, the Company disposed of property and equipment with a gross carrying amount of $19.0 million and accumulated depreciation of $17.0 million. The Company did not dispose of any property and equipment during 2017. Depreciation and amortization expense amounted to $9.9 million, $8.0 million, and $7.6 million in the years ended December 31, 2018, 2017 and 2016, respectively.

The estimated useful life of certain leasehold improvements was re-evaluated and adjusted to reflect the remaining period the Company would expect to have use of those leasehold improvements. As a result of this change in estimate, depreciation expense increased approximately $2.4 million, or $0.03 per share, for the year ended December 31, 2018 as compared to the amount of depreciation expense otherwise calculated based on prior estimates of useful life.

The Company initially recorded certain laboratory equipment asset impairments in the third quarter of 2018 in accordance with ASC 360 Property, Plant and Equipment for assets held-and-used, as the criteria to classify the laboratory equipment as held-for-sale had not been met. The Company identified an indicator of impairment related to this held-and-used laboratory equipment as it was more likely than not that some of its laboratory equipment would be sold or otherwise disposed of significantly before the end of its previously estimated useful life primarily as a result of the restructuring described in Note 14. For the laboratory equipment where its fair value did not exceed its carrying amount, an impairment was recognized. Fair value was estimated utilizing sales of similar equipment, a level 2 fair value measurement. In the fourth quarter of 2018, the Company committed to a plan to actively sell certain of its laboratory equipment. Having met all other criteria, the laboratory equipment met the criteria to classify that equipment as held-for-sale. At December 31, 2018, $1.3 million of laboratory equipment was classified as held-for-sale as reflected in the consolidated balance sheet. The sale is expected to be complete by the end of the first quarter of 2019. Laboratory equipment held-for-sale is reflected at the lower of its carrying amount or fair value less the cost to sell, with any excess recorded as an impairment. In aggregate, impairment losses recognized in connection with laboratory equipment was $3.6 million and included in restructuring costs in the consolidated statement of operations for the year ended December 31, 2018.