All of our intangible assets are subject to amortization and are amortized using the straight-line method over their estimated useful life.

We acquired license and supply agreements in relation to cytisinicline upon the acquisition of Extab Corporation, or Extab, on May 18, 2015. The agreements were determined to have a fair value of $3.1 million with an estimated useful life of 14 years.

	June 30, 2019							December 31, 2018
	Gross Carrying		Accumulated			Net Carrying		Gross Carrying		Accumulated			Net Carrying
	Value		Amortization			Value		Value		Amortization			Value
License Agreements	$	3,117	$	(918	)	$	2,199	$	3,117	$	(807	)	$	2,310

For the three and six months ended June 30, 2019, we recorded license agreement amortization expense of $0.1 million and $0.1 million, respectively. For the three and six months ended June 30, 2018, we recorded license agreement amortization expense of $0.1 million and $0.1 million, respectively. The following table outlines the estimated future amortization expense related to intangible assets held as of June 30, 2019:

Year Ending December 31,
2019	$	112
2020		223
2021		223
2022		223
2023		223
Thereafter		1,195
Total	$	2,199

We evaluate the carrying amount of intangible assets periodically by taking into account events or circumstances that may warrant revised estimates of useful life or that indicate the asset may be impaired. We conducted an analysis of potential impairment indicators for long lived assets, including the license and supply agreements for the active pharmaceutical ingredient cytisinicline, and concluded no impairment has occurred as of June 30, 2019.