Goodwill — As a result of a triggering event in the first quarter of 2020, we fully impaired our remaining goodwill balance, and as a result, we had no goodwill balance as of September 30, 2021. At times when we have a goodwill balance, we are required to evaluate goodwill at least annually as of December 31, or when circumstances require, to determine if the fair value of recorded goodwill has decreased below its carrying value. For impairment testing purposes, goodwill is evaluated at the reporting unit level. Our reporting units for impairment testing are our operating segments. We determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying value after considering qualitative, market and other factors, and if this is the case, any necessary goodwill impairment is determined using a quantitative impairment test. From time to time, we may perform quantitative testing for goodwill impairment in lieu of performing the qualitative assessment. If the resulting fair value of goodwill is less than the carrying value of goodwill, an impairment loss would be recognized for the amount of the shortfall.

Due to the decline in the market price of our common stock and commodity prices in the first quarter of 2020, we lowered our expectations with respect to future activity levels in our contract drilling reporting unit. We performed a quantitative impairment assessment of our goodwill as of March 31, 2020. In completing the assessment, the fair value of our contract drilling operating segment was estimated using the income approach. The estimate of fair value required the use of significant unobservable inputs, representative of a Level 3 fair value measurement. The assumptions included discount rates, revenue growth rates, operating expense growth rates, and terminal growth rates.

Based on the results of the goodwill impairment test as of March 31, 2020, impairment was indicated in our contract drilling reporting unit. We recognized an impairment charge of $395 million in the quarter ended March 31, 2020 associated with the impairment of all of the goodwill in our contract drilling reporting unit.

Intangible Assets — The following table presents the gross carrying amount and accumulated amortization of our intangible assets as of September 30, 2021 and December 31, 2020 (in thousands):


	September 30, 2021							December 31, 2020
	Gross					Net		Gross					Net
	Carrying		Accumulated			Carrying		Carrying		Accumulated			Carrying
	Amount		Amortization			Amount		Amount		Amortization			Amount
Customer relationships	$	1,800	$	(750	)	$	1,050	$	28,000	$	(26,757	)	$	1,243
Developed technology		55,772		(36,613	)		19,159		55,772		(27,515	)		28,257
Internal use software		1,251		(408	)		843		906		(319	)		587
	$	58,823	$	(37,771	)	$	21,052	$	84,678	$	(54,591	)	$	30,087

Amortization expense on intangible assets of approximately $3.1 million and $5.3 million was recorded in the three months ended September 30, 2021 and 2020, respectively. Amortization expense on intangible assets of approximately $9.4 million and $15.9 million was recorded in the nine months ended September 30, 2021 and 2020, respectively.