Number of Unvested Shares of Restricted Stock and Weighted Average Fair Value of Shares at Date of Grant (Detail) (USD $)	9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013
Shares of Restricted Stock
Beginning balance	256,092
Granted	172,915		182,092
Vested	(40,055)	[1]
Forfeited	(26,724)
Ending balance	362,228		182,092
Weighted average fair value of date of grant
Beginning balance	$ 29.83
Granted	$ 26.55		$ 33.10
Vested	$ 23.08	[1]
Forfeited	$ 30.53
Ending balance	$ 28.96		$ 33.10

[1] Includes 7,944 shares which were used to settle minimum employee withholding tax obligations for one employee of approximately $0.2 million in 2014. A net of 32,111 shares of common stock were delivered in the nine months ended September 30, 2014.