7. GOODWILL AND OTHER INTANGIBLE ASSETS

Goodwill was $706,108 as of December 31, 2018, and $101,083 as of September 30, 2018. The increase in goodwill was due to $605,128 in goodwill related to the acquisition of KMG offset by $103 in foreign exchange fluctuations. The amount of goodwill assigned to each of the Electronic Materials and Performance Materials segments was $359,187 and $346,921, respectively.

The components of other intangible assets are as follows:

	December 31, 2018				September 30, 2018
	Gross Carrying Amount		Accumulated Amortization		Gross Carrying Amount		Accumulated Amortization
Other intangible assets subject to amortization:
Product technology, trade secrets and know-how	$	134,335	$	27,684	$	48,825	$	25,305
Acquired patents and licenses		10,570		8,274		8,270		8,252
Customer relationships, trade names, and distribution rights		739,584		24,481		28,068		17,574

Total other intangible assets subject to amortization		884,489		60,439		85,163		51,131

Other intangible assets not subject to amortization:
Other indefinite-lived intangibles*		47,170				1,170
Total other intangible assets not subject to amortization		47,170				1,170

Total other intangible assets	$	931,659	$	60,439	$	86,333	$	51,131

*Other indefinite-lived intangible assets not subject to amortization consist primarily of trade names.

As discussed in Note 4, we recorded $844,800 of intangible assets related to our acquisition of KMG. The allocation of the amount into the various categories of intangible assets, as well as useful lives we have established, are discussed in Note 4.

Amortization expense on our other intangible assets was $9,356 and $1,973 for the three months ended December 31, 2018 and 2017, respectively. Estimated future amortization expense for the five succeeding fiscal years is as follows:

Fiscal Year	Estimated Amortization Expense
Remainder of 2019	$	50,820
2020		87,931
2021		87,228
2022		79,817
2023		67,658

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 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. There were no indicators of potential impairment during the quarter ended December 31, 2018, so it was not necessary to perform an impairment review for goodwill and indefinite-lived intangible assets during the quarter. There have been no impairment charges recorded on the goodwill for any of our reporting units.