Income (Loss) Per Common Share - Computations of Basic and Diluted (Loss) Income Per Common Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Net income, as reported	$ 171,389		$ 143,983		$ 203,910		$ 68,373
Participating basic earnings	(2,868)	[1]	(2,335)	[1]	(3,460)	[1]	(1,124)	[1]
Basic net income attributed to common shareholders	168,521		141,648		200,450		67,249
Reallocation of participating earnings	15	[1]	12	[1]	19	[1]	5	[1]
Diluted net income attributed to common shareholders	$ 168,536		$ 141,660		$ 200,469		$ 67,254
Net income per common share:
Basic	$ 1.04		$ 0.88		$ 1.24		$ 0.42
Diluted	$ 1.04		$ 0.88		$ 1.24		$ 0.42

[1] Restricted Stock Awards represent participating securities because they participate in nonforfeitable dividends or distributions with common equity owners. Income allocable to participating securities represents the distributed and undistributed earnings attributable to the participating securities. Participating securities, however, do not participate in undistributed net losses.