GOODWILL AND OTHER INTANGIBLE ASSETS

A summary of the carrying amount of goodwill attributable to each segment, as well as the changes in such, is as follows:



(in thousands)	Industrial			Widia			Infrastructure			Total
Gross goodwill	$	408,705		$	40,624		$	633,211		$	1,082,540
Accumulated impairment losses	(137,204		)	(13,638		)	(633,211		)	(784,053		)
Balance as of June 30, 2016	$	271,501		$	26,986		$	—		$	298,487

Activity for 2017:
Change in gross goodwill due to translation	1,989			891			—			2,880

Gross goodwill	410,694			41,515			633,211			1,085,420
Accumulated impairment losses	(137,204		)	(13,638		)	(633,211		)	(784,053		)
Balance as of June 30, 2017	$	273,490		$	27,877		$	—		$	301,367

Activity for 2018:
Change in gross goodwill due to translation	764			(329		)	—			435

Gross goodwill	411,458			41,186			633,211			1,085,855
Accumulated impairment losses	(137,204		)	(13,638		)	(633,211		)	(784,053		)
Balance as of June 30, 2018	$	274,254		$	27,548		$	—		$	301,802

The components of our other intangible assets were as follows:



	Estimated Useful Life (in years)	June 30, 2018					June 30, 2017
(in thousands)	Estimated Useful Life (in years)	Gross Carrying Amount		Accumulated Amortization			Gross Carrying Amount		Accumulated Amortization
Contract-based	3 to 15	$	7,061	$	(7,036	)	$	7,064	$	(7,014	)
Technology-based and other	4 to 20	46,666		(30,923		)	46,461		(29,061		)
Customer-related	10 to 21	206,162		(85,301		)	205,502		(74,669		)
Unpatented technology	10 to 30	31,854		(13,096		)	31,754		(10,589		)
Trademarks	5 to 20	12,450		(8,978		)	12,401		(8,648		)
Trademarks	Indefinite	17,609		—			17,326		—
Total		$	321,802	$	(145,334	)	$	320,508	$	(129,981	)

Amortization expense for intangible assets was $14.7 million, $16.6 million and $20.8 million for 2018, 2017 and 2016, respectively. Estimated amortization expense for 2019 through 2023 is $14.1 million, $13.9 million, $13.5 million, $13.1 million, and $12.9 million, respectively.