Intangible Assets

12 Months Ended

Dec. 31, 2018

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible Assets

Intangible Assets

Intangible assets other than goodwill, which are subject to amortization, consist of the following:

	Gross Carrying Amount		Accumulated Amortization			Net Balance
Balance at December 31, 2018
Coal supply agreement	$	84,200	$	(43,684	)	$	40,516
Balance at December 31, 2017
Coal supply agreement	$	84,200	$	(40,646	)	$	43,554

Amortization expense for intangible assets was $3.0 million and $2.1 million in 2018 and 2017, respectively.

Expected annual amortization expense of NACoal's coal supply agreement for the next five years is as follows: $3.0 million in 2019 and $3.1 million in 2020, 2021, 2022 and 2023, respectively. The coal supply agreement is amortized based on units of production over the term of the agreement, which is estimated to be 30 years.