Share-Based Compensation and Other Benefit Plans (Summary of Activity of Service Based Restricted Shares Under LTIP) (Detail) (Service-based restricted stock, USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Service-based restricted stock
Number of Shares
Outstanding at the beginning of the year (in shares)	375,813	286,306	229,722
Granted (in shares)	286,954	293,732	135,223
Vested (in shares)	(281,851)	(197,014)	(68,683)
Forfeited or expired (in shares)	(15,392)	(7,211)	(9,956)
Outstanding at the end of the year (in shares)	365,524	375,813	286,306
Weighted- Average Grant Date Fair Value
Outstanding at the beginning of the year (in dollars per share)		$ 13.71	$ 11.83	$ 12.40
Granted (in dollars per share)	$ 16.70	$ 15.68	$ 11.30
Vested (in dollars per share)	$ 12.69	$ 10.07	$ 11.47
Forfeited or expired (in dollars per share)	$ 14.69	$ 13.38	$ 11.95
Outstanding at the end of the year (in dollars per share)	$ 14.92	$ 13.71	$ 11.83