Other changes included in the above table include minor adjustments for the allocation of certain acquisitions still under measurement. For additional information regarding changes to goodwill resulting from acquisitions, see Note 16, Business Combinations.

We test goodwill for impairment annually during the fourth quarter of our fiscal year or earlier if there is an impairment indicator. We anticipate that the COVID-19 outbreak could have an impact on our customers and the homebuilding industry in general, as it could affect, among other factors, employment levels, consumer spending and consumer confidence, which could decrease demand for homes, adversely affecting our business. As such, we considered whether impairment indicators arose through the date of filing of this Quarterly Report on Form 10-Q for our goodwill, long-lived assets and other intangible assets and concluded that no such factors exist. While we ultimately concluded that our goodwill, long-lived assets and other intangibles assets were not impaired as of March 31, 2020, we will continue to assess impairment indicators related to the impact of the COVID-19 outbreak on our business. Accumulated impairment losses included within the above table were incurred over multiple periods, with the latest impairment charge being recorded during the year ended December 31, 2010.

Intangibles, net

The following table provides the gross carrying amount, accumulated amortization and net book value for each major class of intangibles (in thousands):


	As of March 31,						As of December 31,
	2020						2019
	Gross Carrying Amount		Accumulated Amortization		Net Book Value		Gross Carrying Amount		Accumulated Amortization		Net Book Value
Amortized intangibles:
Customer relationships	$	171,945	$	74,061	$	97,884	$	169,334	$	69,388	$	99,946
Covenants not-to-compete		17,189		11,391		5,798		16,959		10,617		6,342
Trademarks and tradenames		70,891		23,752		47,139		69,718		22,609		47,109
Backlog		14,610		14,005		605		14,080		13,915		165

	$	274,635	$	123,209	$	151,426	$	270,091	$	116,529	$	153,562

The gross carrying amount of intangibles increased approximately $4.5 million during the three months ended March 31, 2020 primarily due to business combinations. For more information, see Note 16, Business Combinations. Remaining estimated aggregate annual amortization expense is as follows (amounts, in thousands, are for the fiscal year ended):


Remainder of 2020	$	19,737
2021		25,086
2022		23,930
2023		21,019
2024		17,504
Thereafter		44,150