Quarterly Data (Unadited) (Tables)

12 Months Ended

Dec. 31, 2012

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Financial Information

(In thousands, except per share data)	2011 Quarter Ended
	March 31		June 30		September 30		December 31
Revenue	$	170,061	$	222,605	$	253,652	$	259,651
Depletion, depreciation and amortization	$	16,063	$	15,660	$	15,628	$	15,027
Operating income	$	40,939	$	49,117	$	44,156	$	20,994
Net income	$	36,192	$	42,698	$	40,741	$	24,664
Comprehensive income attributable to common stockholders	$	36,002	$	42,784	$	40,506	$	24,894
Basic earnings per share attributable to common stockholders	$	0.35	$	0.41	$	0.40	$	0.21
Diluted earnings per share attributable to common stockholders	$	0.34	$	0.39	$	0.37	$	0.21

Quarterly earnings data for the years ended December 31, 2012 and 2011 were as follows:

(In thousands, except per share data)	2012 Quarter Ended
	March 31				June 30				September 30				December 31
	As Reported		As Revised		As Reported		As Revised		As Reported		As Revised
Revenue	$	203,051	$	203,051	$	212,775	$	212,775	$	181,044	$	181,044	$	203,374
Depletion, depreciation and amortization	$	14,672	$	14,672	$	14,862	$	14,862	$	14,107	$	14,107	$	14,374
Operating income	$	1,767	$	1,767	$	13,627	$	13,627	$	9,645	$	9,645	$	18,597
Net income	$	2,439	$	5,940	$	17,829	$	18,797	$	12,692	$	12,803	$	16,876
Comprehensive income attributable to common stockholders	$	2,747	$	6,248	$	18,091	$	19,046	$	13,417	$	13,497	$	17,116
Basic earnings per share attributable to common stockholders	$	0.02	$	0.05	$	0.16	$	0.17	$	0.11	$	0.11	$	0.14
Diluted earnings per share attributable to common stockholders	$	0.02	$	0.05	$	0.15	$	0.17	$	0.11	$	0.11	$	0.13