Intangible Assets, Net

3 Months Ended

Mar. 31, 2020

Goodwill And Intangible Assets Disclosure [Abstract]

Intangible Assets, Net

8. Intangible Assets, net

The following table presents intangible assets (in thousands):

	March 31,			December 31,			Estimated
	2020			2019			useful life
Acquired and in-licensed rights	$	2,262		$	2,262		7 - 21 Years
Capitalized regulatory approval milestones		90,000			90,000		16 Years
Less accumulated amortization		(10,673	)		(9,211	)
Total intangible assets, net	$	81,589		$	83,051

We recorded $1.5 million and $1.4 million in amortization expense related to intangible assets during the three months ended March 31, 2020 and 2019, respectively. Estimated future amortization expense for intangible assets as of March 31, 2020 is as follows (in thousands):

Years ended December 31,	Intangible Assets
Remainder of 2020	$	4,417
2021		5,861
2022		5,856
2023		5,843
2024		5,822
Thereafter		53,790
	$	81,589

The weighted average remaining amortizable life of our patents was 10.7 years at March 31, 2020.

For additional detail of our license agreements with Ionis, see Note 9, License Agreements and Services Agreement with Ionis.