Revenue (Tables)

6 Months Ended

Jun. 30, 2019

Revenue From Contract With Customer [Abstract]

Disaggregation Of Revenue [Table Text Block]

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
United States (1)	$	135,343	$	128,864	$	243,161	$	267,097
South Korea (2)		32,884		70,513		64,706		136,533
Other (2)		224		6,321		5,661		18,377
Total revenue from external customers	$	168,451	$	205,698	$	313,528	$	422,007

(1)The majority of our domestic revenue is attributable to the Owned and Operated Mines segment.

(2)All South Korean revenue and the majority of Other geographical revenue is attributable to our Logistics and Related Activities segment.

Contract With Customer Asset And Liability [Table Text Block]

	June 30,		December 31,
	2019		2018
Trade accounts receivable	$	44,184	$	33,062
Other receivables		753		464
Accounts receivable, net	$	44,937	$	33,527