Intangible assets

12 Months Ended

Dec. 31, 2019

Goodwill And Intangible Assets Disclosure [Abstract]

6.	Intangible assets

Intangible assets are recorded at cost, or when acquired as a part of a business combination, at estimated fair value. These assets are amortized on a straight-line basis over the useful lives of the assets.

		December 31,
(U.S. Dollars, in thousands)	Weighted Average Amortization Period	2019			2018
Cost
Patents	10 years	$	42,034		$	39,085
Developed technology	10 years		39,200			12,400
IPR&D	Indefinite		—			26,800
Customer relationships	9 years		7,430			—
License and other	7 years		15,960			14,654
Trademarks—finite lived	10 years		942			840
	9 years		105,566			93,779
Accumulated amortization
Patents		$	(38,246	)	$	(35,016	)
Developed technology			(4,523	)		(827	)
Customer relationships			(535	)		—
License and other			(7,701	)		(5,744	)
Trademarks—finite lived			(422	)		(295	)
			(51,427	)		(41,882	)
Patents and other intangible assets, net		$	54,139		$	51,897

Intangible assets related to IPR&D projects are considered to be indefinite-lived until the completion or abandonment of the associated research and development efforts. During the period the assets are considered indefinite-lived, they are not amortized but tested for impairment. Impairment testing is performed at least annually or when a triggering event occurs that could indicate a potential impairment. If and when development is complete, which generally occurs when regulatory approval to market a product is obtained, the associated assets are deemed finite-lived and are amortized over a period that best reflects the economic benefits provided by these assets. On February 6, 2019, the Company obtained FDA approval of the M6-C artificial cervical disc for patients suffering from cervical disease degeneration. Following FDA approval, the Company transferred $26.8 million from IPR&D to developed technology, and began amortization over 10 years.

Amortization expense for intangible assets was $7.0 million, $2.7 million and $1.8 million for the years ended December 31, 2019, December 31, 2018 and 2017, respectively. Future amortization expense for intangible assets is estimated as follows:

(U.S. Dollars, in thousands)	Amortization
2020	$	7,420
2021		7,317
2022		7,337
2023		6,668
2024		5,799
Thereafter		19,598
Total	$	54,139