7.	Intangible Assets

Our intangible assets are comprised of both indefinite-lived and finite-lived intangible assets. Intangible assets with indefinite lives and goodwill are not amortized, but are reviewed for impairment at least annually or whenever events or circumstances indicate the carrying value of the asset may not be recoverable. We perform our annual impairment tests of our indefinite-lived intangible assets and goodwill during the fourth quarter of each fiscal year. We also reevaluate the useful life of indefinite-lived intangible assets each reporting period to determine whether events and circumstances continue to support an indefinite useful life. The results of our annual indefinite-lived intangible assets and goodwill impairment assessments in the fourth quarter of 2017 indicated no impairment.

As of both March 31, 2018 and December 31, 2017, our goodwill balance, all of which related to our BA segment, was $0.6 million.

Our intangible assets, other than goodwill, as of March 31, 2018 and December 31, 2017 were as follows (in thousands, except for weighted average remaining useful life):


	Weighted
	Average		As of March 31, 2018							As of December 31, 2017
	Remaining		Gross					Net		Gross					Net
	Useful Life		Carrying		Accumulated			Carrying		Carrying		Accumulated			Carrying
	(in years)		Amount		Amortization			Amount		Amount		Amortization			Amount
Amortized intangible assets:

Software		2.1	$	148,172	$	(98,916	)	$	49,256	$	145,063	$	(93,523	)	$	51,540
Service customer relationship		2.0		8,081		(6,042	)		2,039		8,081		(5,788	)		2,293
Other intangible assets		1.4		1,500		(1,200	)		300		1,500		(1,103	)		397
OEM and dealer relationships				6,724		(6,724	)		—		6,724		(6,724	)		—

Total amortized intangible assets				164,477		(112,882	)		51,595		161,368		(107,138	)		54,230

Unamortized intangible assets:

FCC Licenses				32,283		—			32,283		32,283		—			32,283

Total intangible assets			$	196,760	$	(112,882	)	$	83,878	$	193,651	$	(107,138	)	$	86,513

Amortization expense was $7.6 million and $5.8 million, respectively, for the three month periods ended March 31, 2018 and 2017.

Amortization expense for each of the next five years and thereafter is estimated to be as follows (in thousands):


	Amortization
Years ending December 31,	Expense
2018 (period from April 1 to December 31)	$	19,725
2019	$	17,093
2020	$	9,236
2021	$	3,337
2022	$	1,706
Thereafter	$	498

Actual future amortization expense could differ from the estimated amount as a result of future investments and other factors.