Balance Sheet Account Details

Prepaid expenses and other current assets

The following is a summary of prepaid expenses and other current assets (in thousands):



	December 31,
	2018		2017
Receivables under transition service agreements	$	15,507	$	7,509
Income taxes receivable	2,703		3,806
Prepaid expenses	4,508		2,898
Other	928		162
Total prepaid expenses and other current assets	$	23,646	$	14,375

Inventories

Inventories are stated at the lower of cost (first-in, first-out) or net realizable value. The following is a summary of inventories (in thousands):



	December 31,
	2018		2017
Raw materials	$	24,292	$	22,252
Work-in-process (materials, labor and overhead)	21,280		22,813
Finished goods (materials, labor and overhead)	21,807		22,013
Total inventories	$	67,379	$	67,078

Property, Plant and Equipment

The following is a summary of property, plant and equipment (in thousands):



	December 31,
	2018			2017
Equipment, furniture and fixtures	$	89,285		$	75,728
Building and improvements	37,335			34,994
Leased instruments	42,647			32,458
Land	1,080			1,080
Total property, plant and equipment, gross	170,347			144,260
Less: accumulated depreciation and amortization	(96,446		)	(82,675		)
Total property, plant and equipment, net	$	73,901		$	61,585

The equipment, furniture and fixtures category above includes construction in progress and instruments that have not been placed at a customer under a lease agreement. These items will be reclassified when the assets are placed in service. The total expense for depreciation of fixed assets and amortization of leasehold improvements was $17.7 million, $14.6 million and $13.4 million for the years ended December 31, 2018, 2017 and 2016, respectively. Maintenance and minor repairs are charged to operations as incurred.

Goodwill and Intangible Assets

The Company had goodwill of $337.0 million as of December 31, 2018, which remains consistent with December 31, 2017. Amortizable intangible assets consisted of the following (dollar amounts in thousands):



		December 31, 2018							December 31, 2017
Description	Weighted-average useful life (years)	Gross assets		Accumulated amortization			Net		Gross assets		Accumulated amortization			Net
Purchased technology	9.1	$	112,100	$	(57,495	)	$	54,605	$	112,100	$	(49,614	)	$	62,486
Customer relationships	7.0	122,389		(27,561		)	94,828		122,404		(10,960		)	111,444
License agreements	9.9	6,511		(4,530		)	1,981		6,515		(3,980		)	2,535
Patent and trademark costs	10.8	28,740		(7,624		)	21,116		28,740		(4,917		)	23,823
Software development costs	5.0	6,629		(4,130		)	2,499		6,630		(3,091		)	3,539
Total amortizable intangible assets		$	276,369	$	(101,340	)	$	175,029	$	276,389	$	(72,562	)	$	203,827

Amortization expense related to the capitalized software costs was $1.0 million, $0.8 million and $0.5 million for the years ended December 31, 2018, 2017 and 2016, respectively. Amortization expense (including capitalized software costs) was $28.8 million, $16.1 million and $9.5 million for the years ended December 31, 2018, 2017 and 2016, respectively.

The expected future annual amortization expense of the Company’s intangible assets is as follows (in thousands):



For the years ending December 31,	Amortization expense
2019	$	27,542
2020	27,144
2021	26,999
2022	26,468
2023	25,758
Thereafter	41,118
Total	$	175,029

Other current liabilities

The following is a summary of other current liabilities (in thousands):



	December 31,
	2018		2017
Customer incentives	$	7,516	$	7,165
Accrued interest	347		442
Other	5,129		5,059
Total other current liabilities	$	12,992	$	12,666