Summary of Repurchase Activity under Repurchase Programs (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock Repurchase Program [Line Items]
Repurchases paid, Shares	181,803	137,429	294,059
Repurchases unsettled, Shares	3,399	1,688	538
Prior year authorizations at January 1,	$ 13,963	$ 13,237	$ 15,779
Authorizations	6,036	5,590	5,750
Repurchases paid	(5,130)	(4,815)	(8,272)
Repurchases unsettled	(76)	(49)	(20)
Authorized dollars remaining as of December 31,	$ 14,793	$ 13,963	$ 13,237