Consolidated Statements of Stockholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning Balance at Dec. 31, 2010	$ 2,237,507	$ 1,645	$ 1,734,709	$ (53,848)	$ 561,418	$ (6,417)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income attributable to Arch Coal, Inc.	141,683				141,683
Total comprehensive income (loss)	140,150					(1,533)
Dividends, Common Stock	(80,748)				(80,748)
Dividends on common shares	80,748
Redemption of noncontrolling interest	1,267,933	487	1,267,446
Issuance of shares of common stock under the stock incentive plan — restricted stock and restricted stock units, net of forfeitures		2	(2)
Issuance of shares of common stock under the stock incentive plan — stock options including income tax benefits	2,316	2	2,314
Employee stock-based compensation expense	10,882		10,882
Employee stock-based compensation expense	10,882
Ending Balance at Dec. 31, 2011	3,578,040	2,136	3,015,349	(53,848)	622,353	(7,950)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income attributable to Arch Coal, Inc.	(683,955)				(683,955)
Total comprehensive income (loss)	(692,512)					(8,557)
Dividends, Common Stock	(42,440)				(42,440)
Dividends on common shares	42,440
Redemption of noncontrolling interest			(5,474)
Redemption of noncontrolling interest	(5,474)
Issuance of shares of common stock under the stock incentive plan — restricted stock and restricted stock units, net of forfeitures	0	0	0
Issuance of shares of common stock under the stock incentive plan — stock options including income tax benefits	5,131	5	5,126
Employee stock-based compensation expense	11,822		11,822
Employee stock-based compensation expense	11,822
Ending Balance at Dec. 31, 2012	2,854,567	2,141	3,026,823	(53,848)	(104,042)	(16,507)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income attributable to Arch Coal, Inc.	(641,832)
Total comprehensive income (loss)	(587,633)					54,199
Dividends, Common Stock					(25,475)
Dividends on common shares	25,475
Issuance of shares of common stock under the stock incentive plan — restricted stock and restricted stock units, net of forfeitures	0	0	0
Employee stock-based compensation expense	11,790
Employee stock-based compensation expense	11,790
Ending Balance at Dec. 31, 2013	$ 2,253,249	$ 2,141	$ 3,038,613	$ (53,848)	$ (771,349)	$ 37,692