Earnings Per Share - Reconciliation of Numerators and Denominators Used in Computations of Both Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Basic earnings (loss) per share computation:
Income (loss) from continuing operations	$ (15,136)		$ 415,518		$ (25,891)		$ 362,721
Average common shares	93,797,183		94,164,101		93,916,848		93,533,631
Basic earnings (loss) per share from continuing operations (in dollars per share)	$ (0.16)		$ 4.41		$ (0.28)		$ 3.88
Diluted earnings (loss) per share computation:
Income (loss) from continuing operations	$ (15,136)		$ 415,518		$ (25,891)		$ 362,721
Average common shares	93,797,183		94,164,101		93,916,848		93,533,631
Stock option conversion	0	[1]	805,976	[1]	0	[1]	712,038	[1]
Stock units	0	[2]	367,687	[2]	0	[2]	331,455	[2]
Average common shares — diluted	93,797,183		95,337,764		93,916,848		94,577,124
Diluted earnings (loss) per share from continuing operations (in dollars per share)	$ (0.16)		$ 4.35		$ (0.28)		$ 3.84
Common Stock
Diluted earnings (loss) per share computation:
Anti-dilutive securities excluded	3,421,121		2,949,208		3,638,658		3,758,723
Stock Units
Diluted earnings (loss) per share computation:
Anti-dilutive securities excluded	267,771		8,704		306,176		7,949

[1] Anti-dilutive common shares excluded 3,421,121, 2,949,208, 3,638,658, & 3,758,723

[2] Anti-dilutive stock units excluded 267,771 , 8,704, 306,176, & 7,949