5. Intangible Assets

Indefinite‑life intangible assets consist primarily of gaming licenses. The table below presents the gross carrying value, accumulated amortization, and net book value of each major class of other intangible assets at September 30, 2018 and December 31, 2017:


	September 30, 2018						December 31, 2017
	(in thousands)
	Gross						Gross
	Carrying		Accumulated		Net Book		Carrying		Accumulated		Net Book
	Value		Amortization		Value		Value		Amortization		Value
Indefinite-life intangible assets	$	433,005	$	—	$	433,005	$	375,405	$	—	$	375,405
Other intangible assets		135,555		95,592		39,963		131,483		84,282		47,201
Total	$	568,560	$	95,592	$	472,968	$	506,888	$	84,282	$	422,606

Total other intangible assets increased by $50.4 million for the nine months ended September 30, 2018 primarily due to the purchase of two Category 4 gaming licenses to operate up to 750 slot machines and initially up to 30 table games in York County, Pennsylvania for $50.1 million and in Berks County, Pennsylvania for $7.5 million, partially offset by $11.9 million in amortization of definite-lived intangible assets. Other intangible assets have a weighted average remaining amortization period of approximately 4.2 years.

The Company’s intangible asset amortization expense was $3.3 million and $11.9 million, for the three and nine months ended September 30, 2018, respectively, as compared to $4.3 million and $14.8 million for the three and nine months ended September 30, 2017.

The following table presents expected intangible asset amortization expense based on existing intangible assets as of September 30, 2018 (in thousands):


Remaining 2018	$	2,902
2019		10,200
2020		7,079
2021		4,106
2022		3,635
Thereafter		12,041
Total	$	39,963