Derivatives Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2017

Derivative [Line Items]

Schedule of offsetting and balance sheet presentation

December 31, 2017

Gross Amounts Recognized

Gross Amounts Offset in the Consolidated Balance Sheets

Net Amounts Presented in the Consolidated Balance Sheets

Assets

Liabilities

Assets

Liabilities

Assets

Liabilities

International coal forward contracts

$

—

$

—

$

—

$

—

$

—

$

—

WTI derivative financial instruments

—

—

—

—

—

—

Total

$

—

$

—

$

—

$

—

$

—

$

—

	December 31, 2016
	Gross Amounts Recognized				Gross Amounts Offset in the Consolidated Balance Sheets				Net Amounts Presented in the Consolidated Balance Sheets
	Assets		Liabilities		Assets		Liabilities		Assets		Liabilities
International coal forward contracts	$	—	$	—	$	—	$	—	$	—	$	—
WTI derivative financial instruments		752		—		—		—		752		—
Total	$	752	$	—	$	—	$	—	$	752	$	—

Schedule of derivative mark-to-market (gains) and losses recognized in the consolidated statement of operations and comprehensive income

	2017		2016		2015
International coal forward contracts	$	—	$	(61)	$	4,382
International coal put options		—		—		(5,813)
Domestic coal futures contracts		—		(55)		4,340
WTI derivative financial instruments		2,672		(8,065)		20,229
U.S. On-Highway Diesel derivative financial instruments		—		—		7,496
Net derivative financial instruments loss (gain)	$	2,672	$	(8,180)	$	30,635