Intangible Assets

The following is a summary of other intangible assets included in the Consolidated Condensed Statements of Condition:



	March 31, 2019							December 31, 2018
(Dollars in thousands)	Gross Carrying Amount		Accumulated Amortization			Net Carrying Value		Gross Carrying Amount		Accumulated Amortization			Net Carrying Value
Core deposit intangibles	$	157,150	$	(32,955	)	$	124,195	$	157,150	$	(28,150	)	$	129,000
Customer relationships	77,865		(56,744		)	21,121		77,865		(55,597		)	22,268
Other (a)	5,622		(2,120		)	3,502		5,622		(1,856		)	3,766
Total	$	240,637	$	(91,819	)	$	148,818	$	240,637	$	(85,603	)	$	155,034


(a)	Balance primarily includes noncompete covenants, as well as $.3 million related to state banking licenses not subject to amortization.

Amortization expense was $6.2 million and $6.5 million for the three months ended March 31, 2019 and 2018, respectively. As of March 31, 2019 the estimated aggregated amortization expense is expected to be:



(Dollars in thousands)
Year	Amortization
Remainder of 2019	$	18,625
2020	21,159
2021	19,547
2022	17,412
2023	16,117
2024	14,679

Gross goodwill, accumulated impairments, and accumulated divestiture related write-offs were determined beginning January 1, 2012, when a change in accounting requirements resulted in goodwill being assessed for impairment rather than being amortized. Gross goodwill of $200.0 million with accumulated impairments and accumulated divestiture-related write-offs of $114.1 million and $85.9 million, respectively, were previously allocated to the non-strategic segment, resulting in $0 net goodwill allocated to the non-strategic segment as of March 31, 2019 and December 31, 2018. The regional banking and fixed income segments do not have any accumulated impairments or divestiture related write-offs. The following is a summary of goodwill by reportable segment included in the Consolidated Condensed Statements of Condition as of March 31, 2019 and December 31, 2018.



(Dollars in thousands)	Regional Banking		Fixed Income		Total
December 31, 2017	$	1,243,885	$	142,968	$	1,386,853
Additions (a)	11,648		—		11,648
March 31, 2018	$	1,255,533	$	142,968	$	1,398,501

December 31, 2018	$	1,289,819	$	142,968	$	1,432,787
Additions	—		—		—
March 31, 2019	$	1,289,819	$	142,968	$	1,432,787

(a) See Note 2 - Acquisitions and Divestitures for further details regarding goodwill related to acquisitions.