Goodwill and intangible assets

The changes in the carrying amount of goodwill for the nine months ended March 31, 2019 are as follows:



	Diversified Industrial Segment			Aerospace Systems Segment			Total
Balance at June 30, 2018	$	5,405,771		$	98,649		$	5,504,420
Acquisition	2,940			—			2,940
Foreign currency translation and other	(47,382		)	(13		)	(47,395		)
Balance at March 31, 2019	$	5,361,329		$	98,636		$	5,459,965

The acquisition line represents the goodwill allocation during the measurement period subsequent to the applicable acquisition date.

Intangible assets are amortized on the straight-line method over their legal or estimated useful lives. The following summarizes the gross carrying value and accumulated amortization for each major category of intangible assets:



	March 31, 2019				June 30, 2018
	Gross Carrying Amount		Accumulated Amortization		Gross Carrying Amount		Accumulated Amortization
Patents	$	261,214	$	126,495	$	265,423	$	117,440
Trademarks	542,643		245,339		546,905		227,580
Customer lists and other	2,440,856		1,038,446		2,482,079		933,867
Total	$	3,244,713	$	1,410,280	$	3,294,407	$	1,278,887

Total intangible amortization expense for the nine months ended March 31, 2019 was $156,527. The estimated amortization expense for the five years ending June 30, 2019 through 2023 is $196,201, $185,541, $180,945, $175,094 and $167,601, respectively.

Intangible assets are evaluated for impairment whenever events or circumstances indicate that the undiscounted net cash flows to be generated by their use over their expected useful lives and eventual disposition may be less than their net carrying value. No material intangible asset impairments occurred during the nine months ended March 31, 2019.