Summary of Repurchase Activity under Repurchase Programs (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Stock Repurchase Program [Line Items]
Repurchases paid, Shares	756,143	[1]	773,258	[1]	363,606	[1]
Repurchases unsettled, Shares	13,983	[1]	6,282	[1]	6,798	[1]
Prior year authorizations at January 1,	$ 14,433		$ 14,793		$ 13,963
Authorizations	14,410		12,164		6,036
Repurchases paid	(15,264)		(12,370)		(5,130)
Repurchases unsettled	(295)		(154)		(76)
Authorized dollars remaining as of December 31,	$ 13,284		$ 14,433		$ 14,793

[1] The number of shares outstanding for all prior periods has been retroactively restated to reflect the Company's two-for-one common stock split effected in the form of a common stock dividend distributed on April 1, 2014.