Consolidated Statement of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities:
Net income	[1]	$ 33,076	$ 12,510	$ 20,132
Deferred income taxes		(16,446)	(3,859)	7,452
Equity (income) loss		(365)	1,436	1,606
Cash distributions		175	3,977
DD&A		38,495	35,565	43,942
Asset impairment			16,560
Loss on sale of assets		45	197
Change in fair value of interest rate swaps		(723)	(637)	159
Amortization and write off deferred financing costs		1,829	2,325	1,394
Amortization of purchased coal contracts		8,922	1,593
Accretion of ARO		861	1,029	498
Share-based compensation		7,266	2,539	3,134
Taxes paid on vesting of RSUs		(3,204)	(1,098)	(1,029)
Change in current assets and liabilities:
Accounts receivable		5,533	(5,632)	10,627
Coal inventory		(2,704)	4,815	4,807
Parts and supply inventory		48	1,164	3,664
Prepaid income taxes		(3,226)	5,312	448
Accounts payable and accrued liabilities		(815)	(11,193)	(1,686)
Prepaid expense		(4,823)	(2,567)	370
Other		(2,376)	(3,118)	(862)
Cash provided by operating activities		61,568	60,918	94,656
Investing activities:
Capital expenditures		(28,622)	(19,832)	(31,167)
Proceeds from the sale of equipment		506
Purchase of mining assets			(22,358)
Proceeds from maturities of certificates of deposit		5,820
Purchase of certificates of deposit			(7,315)
Other			189	641
Cash used in investing activities		(22,296)	(49,316)	(30,526)
Financing activities:
Payments on bank debt		(36,625)	(34,855)	(56,875)
Bank borrowings			24,000
Deferred financing costs			(2,090)
Proceeds from bulldog property		4,940
Dividends		(4,892)	(4,799)	(4,794)
Cash used in financing activities		(36,577)	(17,744)	(61,669)
Increase (decrease) in cash and cash equivalents		2,695	(6,142)	2,461
Cash and cash equivalents, beginning of year		9,788	15,930	13,469
Cash and cash equivalents, end of year		12,483	9,788	15,930
Supplemental Cash Flow Information [Abstract]
Cash paid for interest		11,663	12,429	14,149
Cash paid for income taxes		1,562
Cash received for income taxes, net			(5,594)	(956)
Capital expenditures included in accounts payable		$ 7,615		$ 804
Capital expenditures included in accounts payable, net			$ (1,616)

[1] There is no material difference between net income and comprehensive income.