PROPERTY AND EQUIPMENT

12 Months Ended

Dec. 31, 2017

Property Plant And Equipment [Abstract]

PROPERTY AND EQUIPMENT

9. PROPERTY AND EQUIPMENT

Property and equipment are recorded at historical cost, net of accumulated depreciation. The following table summarizes components of property and equipment, net for each of the periods indicated:

	As of December 31,
	2017			2016
	(in thousands)
Land	$	4,158		$	4,158
Building and improvements		14,543			12,729
Software and computer equipment		8,965			6,775
Lab equipment		9,860			14,149
Office equipment		2,211			3,028
Leasehold improvements		13,633			22,872
Construction in progress		7,808			4,436
Property and equipment, gross		61,178			68,147
Less: accumulated depreciation		(18,022	)		(30,346	)
Property and equipment, net	$	43,156		$	37,801

For the years ended December 31, 2017, 2016 and 2015, depreciation expense totaled $6.4 million, $5.0 million and $4.7 million, respectively. The decrease in accumulated depreciation related to write-offs of fully deprecated property and equipment that the Company no longer uses as of December 31, 2017. The cost basis of these assets is approximately $17.1 million. No loss was recognized. Included in the $30.3 million accumulated depreciation as of December 31, 2016 was $0.8 million of accelerated depreciation for certain assets whose expected useful lives were shortened due to the Corvallis plan (defined in Note 11).