6. Goodwill and Intangible Assets

Goodwill represents the excess of net book value over the estimated fair value of net tangible and identifiable intangible assets of a reporting unit. Goodwill is tested for impairment annually or more often if impairment indicators are present at the reporting unit level. If events occur or circumstances change that would more likely than not reduce fair values of the reporting units below their carrying values, goodwill will be evaluated for impairment between annual tests. No triggering events indicating goodwill impairment occurred during the six months ended March 31, 2019. Please refer to Note 7, "Goodwill and Intangible Assets" to the Company's consolidated financial statements included in the 2018 Annual Report on Form 10-K for further information on the goodwill impairment testing performed during fiscal year 2018.

The components of the Company’s goodwill by operating segment at March 31, 2019 and September 30, 2018 are as follows (in thousands):


	Brooks
	Semiconductor
	Solutions		Brooks
	Group		Life Sciences		Other		Total
Gross goodwill, at September 30, 2018	$	636,907	$	207,913	$	26,014	$	870,834
Accumulated goodwill impairments		(588,944)		—		(26,014)		(614,958)
Goodwill, net of accumulated impairments, at September 30, 2018		47,963		207,913		—		255,876
Acquisitions and adjustments		(184)		236,834		—		236,650
Gross goodwill, at March 31, 2019		636,723		444,747		26,014		1,107,484
Accumulated goodwill impairments		(588,944)		—		(26,014)		(614,958)
Goodwill, net of accumulated impairments, at March 31, 2019	$	47,779	$	444,747	$	—	$	492,526

During the six months ended March 31, 2019, the Company recorded a goodwill increase of $236.8 million primarily related to the acquisition of GENEWIZ. Please refer to Note 5 "Acquisitions" for further information on this transaction.

The components of the Company’s identifiable intangible assets as of March 31, 2019 and September 30, 2018 are as follows (in thousands):


	March 31, 2019						September 30, 2018
			Accumulated		Net Book				Accumulated		Net Book
	Cost		Amortization		Value		Cost		Amortization		Value
Patents	$	5,302	$	4,477	$	825	$	5,302	$	4,325	$	977
Completed technology		88,724		33,592		55,132		44,829		28,934		15,895
Trademarks and trade names		25,318		4,225		21,093		6,298		2,953		3,345
Customer relationships		267,372		73,629		193,743		142,489		62,750		79,739
	$	386,716	$	115,923	$	270,793	$	198,918	$	98,962	$	99,956

Amortization expense for intangible assets was $17.2 million and $11.1 million, respectively, during the six months ended March 31, 2019 and 2018.

Estimated future amortization expense for the intangible assets for the remainder of fiscal year 2019, the subsequent four fiscal years and thereafter is as follows (in thousands):


Fiscal year ended September 30,
2019	$	17,993
2020		41,339
2021		37,546
2022		34,545
2023		31,589
Thereafter		107,781
	$	270,793