STOCKHOLDERS' EQUITY AND ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Additional Information (Detail) (USD $)	12 Months Ended			0 Months Ended	2 Months Ended
	Dec. 31, 2014 class_of_stock	Dec. 31, 2013	Dec. 31, 2012	Jul. 16, 2014	Feb. 25, 2015
Class of Stock [Line Items]
Number of classes of capital stock	2
Common stock, par value (in USD per share)	$ 2.50	$ 2.50
Preferred dividends paid	$ 859,000	$ 1,360,000	$ 1,360,000
Proceeds from issuance of common shares	56,473,000	0	0
Preferred Stock [Member]
Class of Stock [Line Items]
Cumulative dividends paid on Series A Convertible Exchangeable Preferred Stock (in USD per share)	$ 2.125
Preferred stock, redemption value (in USD per share)	$ 100.00
Conversion of stock, shares converted (shares)	68,291
Common Stock [Member]
Class of Stock [Line Items]
Conversion of stock, shares issued (shares)	466,537
Shares issued in public offering (shares)				1,684,507
Shares issued in public offering, price per share (in USD per share)				$ 35.50
Proceeds from issuance of common shares				59,800,000
Stock issued in public offering, brokerage fees (in USD per share)				$ 1.775
Stock issued in public offering, brokerage fees				3,000,000
Legal and other fees associated with the public offering				300,000
Subsequent Event [Member] | Preferred Stock [Member]
Class of Stock [Line Items]
Conversion of stock, shares converted (shares)					88,369
Shares redeemed (shares)					3,175
Shares issued for redeemed stock (shares)					300,000.0
Subsequent Event [Member] | Common Stock [Member]
Class of Stock [Line Items]
Conversion of stock, shares issued (shares)					603,713
Westmoreland Resource Partners LP [Member]
Class of Stock [Line Items]
Restricted net assets not available for transfer	$ 73,000,000