FIXED ASSETS

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



	December 31,
	2017			2016
Machinery and laboratory equipment	$	39,002		$	34,309
Leasehold improvements	34,933			33,787
Computer equipment and software	7,086			5,623
Office furniture and equipment	1,603			1,606
Construction in progress	73,632			63,201
Total	156,256			138,526
Less: accumulated depreciation	(49,210		)	(37,510		)
Fixed assets, net	$	107,046		$	101,016

Depreciation expense for the years ended December 31, 2017, 2016 and 2015 was $13.8 million, $12.8 million and $11.2 million, respectively. During the years ended December 31, 2017, 2016 and 2015, the Company capitalized interest of $1.1 million, $1.5 million and $0.8 million, respectively.

As of December 31, 2017 and 2016, total fixed assets, net, includes leasehold improvements and manufacturing process equipment located in England in the amount of $59.8 million and $33.7 million, respectively.

As of December 31, 2017 and 2016, the Company had an ARO of $1.5 million and $0.5 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 2017 relates to a $0.5 million revision in estimated future cash flows related to the AROs, $0.4 million of liabilities incurred in the current period and $0.1 million of accretion expense.