Goodwill and Other Intangible Assets

The changes in the net carrying amount of goodwill for the nine months ended September 30, 2018 are as follows:



Balance as of December 31, 2017	$	401,954

Foreign currency translation	(977		)

Balance as of September 30, 2018	$	400,977

Assets and liabilities of acquired businesses are recorded at their estimated fair values as of the date of acquisition. Goodwill represents costs in excess of fair values assigned to the underlying net assets of acquired businesses.

Other intangible assets consist of the following:



	September 30, 2018						December 31, 2017
	Weighted Average Amortization Period (Years)	Gross Carrying Amount		Accumulated Amortization			Gross Carrying Amount		Accumulated Amortization
Amortized intangible assets:

Customer and distributor relationships	29	$	214,598	$	(94,371	)	$	214,685	$	(86,137	)

Sales representation, marketing and promotional rights	25	149,376		(40,500		)	149,376		(36,000		)

Patents and other intangible assets	15	61,292		(43,700		)	69,668		(42,127		)

Developed technology	16	88,132		(6,180		)	62,283		(3,352		)

Unamortized intangible assets:

Trademarks and tradenames		86,544		—			86,544		—

	24	$	599,942	$	(184,751	)	$	582,556	$	(167,616	)

Customer and distributor relationships, trademarks and tradenames, developed technology and patents and other intangible assets primarily represent allocations of purchase price to identifiable intangible assets of acquired businesses. Sales representation, marketing and promotional rights represent intangible assets created under our agreement with Musculoskeletal Transplant Foundation (“MTF”).

Amortization expense related to intangible assets which are subject to amortization totaled $6.0 million and $5.3 million in the three months ended September 30, 2018 and 2017, respectively, and $17.2 million and $15.6 million in the nine months ended September 30, 2018 and 2017, respectively, and is included as a reduction of revenue (for amortization related to our sales representation, marketing and promotional rights) and in selling and administrative expense (for all other intangible assets) in the consolidated condensed statements of comprehensive income. Included in developed technology is $25.8 million of earn-out consideration that is considered probable as of September 30, 2018 associated with a prior asset acquisition. This is recorded in other current liabilities at September 30, 2018. This acquired developed technology has a weighted average useful life of 14 years. During the three months ended September 30, 2018, the Company wrote off $9.5 million related to an in-process research and development asset and recorded the net charge to research and development expense. Refer to Notes 11 and 13 for further details.

The estimated intangible asset amortization expense remaining for the year ending December 31, 2018 and for each of the five succeeding years is as follows:



	Amortization included in expense		Amortization recorded as a reduction of revenue		Total
Remaining, 2018	$	4,493	$	1,500	$	5,993
2019	17,622		6,000		23,622
2020	17,639		6,000		23,639
2021	16,686		6,000		22,686
2022	15,227		6,000		21,227
2023	14,615		6,000		20,615