Stock-Based Compensation Expense - Summary of Changes in Stock Options Outstanding (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options outstanding beginning balance at December 31, 2012, Number of Shares	56,042
Granted, Number of Shares	6,247
Exercised, Number of Shares	(2,192)
Canceled, Number of Shares	(1,006)
Options outstanding ending balance at March 31, 2013, Number of Shares	59,091
Options exercisable at March 31, 2013, Number of Shares	39,726
Options outstanding, beginning balance at December 31, 2012, Weighted-Average Exercise Price Per Share	$ 5.75
Granted, Weighted-Average Exercise Price Per Share	$ 6.89
Exercised, Weighted-Average Exercise Price Per Share	$ 3.72
Canceled, Weighted-Average Exercise Price Per Share	$ 8.24
Options outstanding, ending balance at March 31, 2013, Weighted-Average Exercise Price Per Share	$ 5.90
Options exercisable at March 31, 2013, Weighted-Average Exercise Price Per Share	$ 5.87
Options outstanding at March 31, 2013, Weighted-Average Remaining Contractual Term	3 years 10 months 10 days
Options exercisable at March 31, 2013, Weighted-Average Remaining Contractual Term	2 years 8 months 19 days
Options outstanding at March 31, 2013, Aggregate Intrinsic Value	$ 85,227
Options exercisable at March 31, 2013, Aggregate Intrinsic Value	$ 62,059