Summary of Shares of Outstanding Restricted Stock Units and Restricted Stock Awards Activity (Detail)	9 Months Ended
	Sep. 30, 2012
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding at January 1, 2012	1,671,962	[1]
Granted	590,889	[1]
Delivered	(114,213)	[1]
Forfeited	(25,763)	[1]
Outstanding at September 30, 2012	2,122,875	[1]
Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding at January 1, 2012	317,092
Delivered	(104,912)
Forfeited	(12,667)
Outstanding at September 30, 2012	199,513

[1] The outstanding restricted stock units include approximately $1.5 million restricted stock units which are vested, but the underlying shares of stock have not yet been delivered. Delivery of the underlying shares of stock for these vested units will occur on the earlier of December 31, 2014 or the date on which the employee ceases to be employed by, or provide services to, the Company, unless the employee elected optional early delivery. There is one remaining optional early delivery date in 2013.