Stock Awards - Additional Information (Detail) (USD $)	6 Months Ended		12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012	Jun. 30, 2011	Jun. 30, 2010	Sep. 09, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock, authorized (shares)	600,000,000		600,000,000
Shares of common stock reserved for issuance			53,950,960
Compensation expense recognized, vesting term			48 months
Stock options vesting period			4 years
Options granted, exercisable period			10 years
Stock options subject to performance-based						275,808
Term of certain board-approved financial performance targets			1 year
Target achieved by executive officer			98.00%
Stock options eligible to vest			243,744
Stock-based compensation expense	$ 5,637,000	$ 1,121,000	$ 27,937,000	$ 2,954,000	$ 545,000
Weighted-average grant date fair value of options granted (usd per share)	$ 2.52		$ 7.68	$ 1.16	$ 0.61
Fair value of vested shares	2,600,000		19,200,000	2,000,000	300,000
Total unrecognized compensation cost, adjusted for estimated forfeitures, related to unvested stock options			76,000,000
Weighted-average remaining vesting period for unvested stock options			2 years 7 months 24 days
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense recognized, vesting term			4 years
Weighted-average remaining vesting period for unvested stock options			3 years 4 months 17 days
Unrecognized compensation expense expected to be recognized			16,800,000
Annual vesting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense recognized, vesting term			1 year
Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting period			3 years
Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			$ 1,300,000
2005 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock, authorized (shares)			55,592,864
Stock options granted to new employees vest, percentage per annum			25.00%
Stock options granted description			Stock options granted under our 2005 Stock Plan and the 2012 Plan to new employees generally vest 25% one year from the date the requisite service period begins and continue to vest monthly for each month of continued employment over the remaining three years. Options granted to members of our board of directors and to existing employees generally vest in 48 equal monthly installments. Options granted to members of our board of directors starting in June 2012 generally vest in 36 equal monthly installments. Options granted generally are exercisable for a period of up to 10 years.
2012 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock, authorized (shares)			13,587,576
Number of shares of common stock outstanding, increase, percentage			5.00%
Number of shares of common stock reserved for issuance, increase, description			January 1 of each calendar year, from January 1, 2013 through January 1, 2022, by up to 5% of the total number of shares of the common stock outstanding on December 31 of the preceding calendar year
2012 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock outstanding, increase, percentage			1.00%
Shares of common stock reserved for issuance			5,000,000
Number of shares of common stock reserved for issuance, increase, description			January 1 of each calendar year, from January 1, 2013 through January 1, 2022, by up to 1% of the total number of shares of the common stock outstanding on December 31 of the preceding calendar year
Purchase price of common stock, percent			85.00%
Shares issued under 2012 ESPP			0
2005 Stock Plan and 2012 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted to new employees vest, percentage per annum			25.00%
Requisite service period to vest employment continuation period			3 years
2005 Stock Plan and 2012 Plan [Member] | Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Requisite service period to vest employment continuation period			3 years