FIXED ASSETS

Fixed assets, net, summarized by major category, consist of the following (in thousands):



	December 31,
	2018			2017
Machinery and laboratory equipment	$	67,431		$	39,002
Leasehold improvements	57,955			34,933
Computer equipment and software	8,131			7,086
Office furniture and equipment	1,548			1,603
Construction in progress	35,163			73,632
Total	170,228			156,256
Less: accumulated depreciation	(61,558		)	(49,210		)
Fixed assets, net	$	108,670		$	107,046

Depreciation expense for the years ended December 31, 2018, 2017 and 2016 was $13.2 million, $13.8 million and $12.8 million, respectively. During the years ended December 31, 2018, 2017 and 2016, the Company capitalized interest of $0.7 million, $1.1 million and $1.5 million, respectively.

As of December 31, 2018 and 2017, total fixed assets, net, includes leasehold improvements and manufacturing process equipment located in England in the amount of $64.6 million and $59.8 million, respectively.

As of December 31, 2018 and 2017, the Company had AROs of $2.2 million and $1.5 million, respectively, included in other liabilities on its consolidated balance sheet, for costs associated with returning leased space to its original condition upon the termination of certain lease agreements. The increase in 2018 related to a $0.4 million revision in estimated future cash flows related to the AROs and $0.1 million of accretion expense.