Summary of Total Compensation Expense Recognized in Statements of Operations for Stock-Based Compensation (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 971	$ 4,518	$ 10,856	$ 21,077
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	(144)	210	476	1,207
Stock awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	657	3,862	8,499	17,969
Company expense on ESPP discount
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 458	$ 446	$ 1,881	$ 1,901