Income 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
	Mar. 31, 2015		Mar. 31, 2014
Earnings Per Share Reconciliation [Abstract]
Net income, as reported	$ 27,684		$ 32,521
Participating earnings	(463)	[1]	(560)	[1]
Basic net income attributed to common shareholders	27,221		31,961
Reallocation of participating earnings	0	[1]	3	[1]
Diluted net income attributed to common shareholders	$ 27,221		$ 31,964
Net income per common share:
Basic	$ 0.16		$ 0.20
Diluted	$ 0.16		$ 0.20

[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.