Related-Party Transactions - Summary of Certain Affiliate Amounts Included in Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Due from affiliates - current		$ 38,658	$ 49,613
Financing receivables - affiliate - current		3,459	3,392
Prepaid royalties - affiliate - current		1,619	2,000
Due to affiliates - current		16,304	17,740
Murray Energy And Affiliated Entities | Affiliate
Related Party Transaction [Line Items]
Due from affiliates - current	[1]	38,658	49,613
Financing receivables - affiliate - current		3,459	3,392
Financing receivables - affiliate - noncurrent		59,815	60,705
Due to affiliates - current	[1]	14,668	15,924
Foresight Reserves and Affiliated Entities | Affiliate
Related Party Transaction [Line Items]
Prepaid royalties - affiliate - current		1,619	2,000
Due to affiliates - current		$ 1,636	$ 1,816

[1] Includes amounts due to/from Javelin, a joint venture partially owned by Murray Energy.