Goodwill

The changes in the carrying amount of goodwill for the year ended September 30, 2018 are as follows (in thousands):



	Solar			Semiconductor		Polishing		Total
Goodwill	$	6,962		$	5,063	$	728	$	12,753
Accumulated impairment losses	(1,348		)	—		—		(1,348		)
Balance at September 30, 2017	5,614			5,063		728		11,405
Impairment of goodwill	(5,663		)	—		—		(5,663		)
Net exchange differences	49			842		—		891
Balance at September 30, 2018	$	—		$	5,905	$	728	$	6,633

Goodwill	$	6,836		$	5,905	$	728	$	13,469
Accumulated impairment losses	(6,836		)	—		—		(6,836		)
Balance at September 30, 2018	$	—		$	5,905	$	728	$	6,633

During 2018, we periodically assessed whether any indicators of impairment existed which would require us to perform an interim impairment review. As of each interim period end during the year, we concluded that a triggering event had not occurred that would more likely than not reduce the fair value of our reporting units below their carrying values. We performed our annual test of goodwill for impairment during the fourth quarter of 2018. The results of the first step of the goodwill impairment test indicated that the fair value of our Semiconductor reporting unit was in excess of its carrying value, and, thus, we did not require an impairment charge. However, we identified the need for a goodwill impairment charge in our Solar segment of $5.7 million, due primarily to the decline in our expected performance of that segment. While the quantitative analysis indicated no impairment of Semiconductor segment goodwill existed as of September 30, 2018, if the future performance of this reporting unit falls short of our expectations or if there are significant changes in operations due to changes in market conditions, we could be required to recognize material impairment charges in future periods.