Number and Cost of Employee Stock Plan Repurchases (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stockholders Equity Note [Line Items]
Employee stock plan repurchased (in shares)	1,661	1,020	2,084
Employee stock plan repurchased	$ 50,045	$ 29,017	$ 59,164