Note 4. Goodwill and Intangible Assets

The following table presents changes in goodwill, all of which has been allocated to the GDSO segment (in thousands):


Balance at December 31, 2017	$	312,401
Acquisition of Cheshire (1)		527
Acquisition of Champlain (1)		18,478
Acquisition of Honey Farms—change in goodwill (1)		(139)
Dispositions (2)		(3,861)
Balance at December 31, 2018	$	327,406

(1)

See Note 19 for information on the Partnership’s business combinations.

(2)

Dispositions represent derecognition of goodwill associated with the sale and disposition of certain assets (see Note 6).

Intangible assets consisted of the following (in thousands):


	Gross				Net
	Carrying		Accumulated		Intangible		Amortization
	Amount		Amortization		Assets		Period
At December 31, 2018
Intangible assets subject to amortization:
Terminalling services	$	26,365	$	(15,093)	$	11,272	20 years
Customer relationships		43,986		(41,195)		2,791	2-15 years
Supply contracts		87,578		(46,430)		41,148	5-15 years
Favorable leasehold interests		3,380		(3,045)		335	2-5 years
Brand incentive program		1,445		(1,445)		—	5 years
Other intangible assets		5,195		(2,209)		2,986	1-20 years
Total intangible assets	$	167,949	$	(109,417)	$	58,532
At December 31, 2017
Intangible assets subject to amortization:
Terminalling services	$	26,365	$	(13,758)	$	12,607	20 years
Customer relationships		43,986		(40,760)		3,226	2-15 years
Supply contracts		77,771		(38,800)		38,971	5-15 years
Favorable leasehold interests		3,380		(2,717)		663	2-5 years
Brand incentive program		1,445		(1,421)		24	5 years
Other intangible assets		1,729		(675)		1,054	20 years
Total intangible assets	$	154,676	$	(98,131)	$	56,545

The aggregate amortization expense was approximately $11.0 million, $9.2 million and $9.4 million for the years ended December 31, 2018, 2017 and 2016, respectively. In addition, the Partnership recognized amortization expense related to leasehold interests of $0.3 million, $0.6 million and $1.3 million in 2018, 2017 and 2016, respectively. The decrease in amortization expense in 2017 compared to 2016 was due to intangible assets that became fully amortized during 2017.

The estimated annual intangible asset amortization expense for future years ending December 31 is as follows (in thousands):


2019	$	11,857
2020		11,074
2021		10,349
2022		7,198
2023		6,768
Thereafter		11,286
Total intangible assets	$	58,532