Share-Based Compensation - Summary of Stock Option Activity (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options outstanding, Beginning Balance, Shares	363,896
Exercised, Shares	(47,343)
Forfeited or Expired, Shares	(27,419)
Options outstanding, Ending Balance, Shares	289,134
Options outstanding, Beginning Balance, Weighted Average Exercise Price	$ 22.03
Exercised, Weighted Average Exercise Price	$ 19.48
Forfeited or Expired, Weighted Average Exercise Price	$ 28.22
Options outstanding, Ending Balance, Weighted Average Exercise Price	$ 21.87
Options outstanding, Beginning Balance, Options Exercisable	276,009
Options outstanding, Ending Balance, Options Exercisable	287,134