6. GOODWILL AND OTHER INTANGIBLE ASSETS

Goodwill was $101,083 and $101,932 as of September 30, 2018 and 2017, respectively. The decrease in goodwill was due to $154 in foreign exchange fluctuations of the New Taiwan dollar and a $695 decrease related to the sale of certain ESF assets. As a result of this sale of assets in March 2018, we received net proceeds of $3,277, of which $250 is held in escrow, and recorded a gain of $956 in other income in the Consolidated Statements of Income.

The components of other intangible assets are as follows:

	September 30, 2018				September 30, 2017
	Gross Carrying Amount		Accumulated Amortization		Gross Carrying Amount		Accumulated Amortization
Other intangible assets subject to amortization:
Product technology	$	46,275	$	22,755	$	42,287	$	17,604
Acquired patents and licenses		8,270		8,252		8,270		8,241
Trade secrets and know-how		2,550		2,550		2,550		2,550
Customer relationships, distribution rights and other		28,068		17,574		28,229		15,421

Total other intangible assets subject to amortization		85,163		51,131		81,336		43,816

Other intangible assets not subject to amortization:
In-process technology		-				4,000
Other indefinite-lived intangibles*		1,170				1,190
Total other intangible assets not subject to amortization		1,170				5,190

Total other intangible assets	$	86,333	$	51,131	$	86,526	$	43,816

Other indefinite-lived intangibles not subject to amortization primarily consist of trade names.

During the first quarter of fiscal 2018, development of our in-process technology was completed, and we reclassified $4,000 to product technology under other intangible assets subject to amortization.

Amortization expense was $7,495, $7,795 and $8,176 for fiscal 2018, 2017 and 2016, respectively. Estimated future amortization expense of intangible assets as of September 30, 2018 for the five succeeding fiscal years is as follows:

Fiscal Year	Estimated Amortization Expense

2019	$	7,119
2020		7,115
2021		7,108
2022		7,108
2023		1,717

Goodwill and indefinite-lived intangible assets are tested for impairment annually in the fourth quarter of our fiscal year or more frequently if indicators of potential impairment exist, using a fair-value-based approach. The recoverability of goodwill is measured at the reporting unit level, which is defined as either an operating segment or one level below an operating segment. An entity has the option to assess the fair value of a reporting unit either using a qualitative analysis ("step zero") or a quantitative analysis ("step one"). Similarly, an entity has the option to use a step zero or a step one approach to determine the recoverability of indefinite-lived intangible assets. In fiscal 2017 and 2018, we chose to use a step one analysis for both goodwill impairment and for indefinite-lived intangible asset impairment, with the exception of our CMP slurries reporting unit, for which we chose to use a step zero analysis for fiscal 2018.

We completed our annual impairment test during our fourth quarter of fiscal 2018 and concluded that no impairment existed. No impairment existed as a result of our impairment test during the fourth quarter of fiscal 2017. During the fourth quarter of fiscal 2016, we recorded $1,000 of impairment expense on one of the in-process technology assets acquired in the NexPlanar acquisition based on management's revised expected future cash flows for this asset. The impairment charge was included in research, development and technical expenses on our Consolidated Statements of Income. We concluded that no other impairment of goodwill or intangible assets was necessary. There have been no cumulative impairment charges recorded on the goodwill for any of our reporting units.