Intangible assets

12 Months Ended

Dec. 31, 2020

Goodwill And Intangible Assets Disclosure [Abstract]

7.	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, which the Company believes is materially consistent with the pattern of economic benefit provided by these assets.

		December 31,
(U.S. Dollars, in thousands)	Weighted Average Amortization Period	2020			2019
Cost
Patents	10 years	$	50,326		$	42,034
Developed technology	10 years		44,334			39,200
IPR&D	Indefinite		300			—
Customer relationships	7 years		15,685			7,430
License and other	8 years		16,941			15,960
Trademarks—finite lived	10 years		1,812			942
	9 years		129,398			105,566
Accumulated amortization
Patents		$	(46,272	)	$	(38,246	)
Developed technology			(8,925	)		(4,523	)
Customer relationships			(2,095	)		(535	)
License and other			(11,006	)		(7,701	)
Trademarks—finite lived			(583	)		(422	)
			(68,881	)		(51,427	)
Intangible assets, net		$	60,517		$	54,139

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 $11.2 million, $7.0 million and $2.7 million for the years ended December 31, 2020, December 31, 2019 and 2018, respectively. Future amortization expense for intangible assets is estimated as follows:

(U.S. Dollars, in thousands)	Amortization
2021	$	9,292
2022		9,143
2023		8,488
2024		8,020
2025		7,001
Thereafter		18,273
Total finite-lived intangible assets, net	$	60,217
Indefinite-lived intangible assets, net		300
Intangible assets, net	$	60,517