Stock Awards - Summary of stock option activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended	12 Months Ended
Dec. 31, 2011	Dec. 31, 2012	Jun. 30, 2011	Jun. 30, 2010
Summary of stock option activity
Number of Shares, Outstanding, Beginning Balance	26,326,394	39,601,640	16,520,984	19,164,000
Number of Shares, Granted	17,055,120	7,695,730	15,402,456	4,684,000
Number of Shares, Exercised	(1,469,118)	(6,654,558)	(4,279,456)	(7,036,768)
Number of Shares, Forfeited	(2,310,756)	(4,187,185)	(867,590)	(290,248)
Number of shares, Cancelled		(340,167)	(450,000)
Number of Shares, Outstanding, Ending Balance	39,601,640	36,115,460	26,326,394	16,520,984
Number of Shares, Vested and expected to vest		35,427,432
Number of Shares, Vested and exercisable		13,155,248
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Weighted-Average Exercise Price, Outstanding, Beginning Balance, usd per share	$ 1.40	$ 2.20	$ 0.34	$ 0.07
Weighted-Average Exercise Price, Granted, usd per share	$ 3.29	$ 15.03	$ 2.15	$ 1.00
Weighted-Average Exercise Price, Exercised, usd per share	$ 1.45	$ 0.76	$ 0.25	$ 0.03
Weighted-Average Exercise Price, Forfeited, usd per share	$ 1.61	$ 3.47	$ 0.87	$ 0.41
Weighted-Average Exercise Price Cancelled, usd per share		$ 1.90	$ 0.18
Weighted-Average Exercise Price, Outstanding, Ending Balance, usd per share	$ 2.20	$ 5.05	$ 1.40	$ 0.34
Weighted-Average Exercise Price, Vested and expected to vest, usd per share		$ 4.99
Weighted-Average Exercise Price, Vested and exercisable, usd per share		$ 2.11
Weighted-Average Remaining Contractual Life		8 years 3 months 23 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest		8 years 3 months 20 days
Weighted-Average Remaining Contractual Term, Vested and exercisable		7 years 6 months 27 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value	$ 2,380	$ 84,215	$ 7,489	$ 10,054
Aggregate Intrinsic Value, Outstanding		905,846
Aggregate Intrinsic Value, Vested and expected to vest		890,661
Aggregate Intrinsic Value, Vested and exercisable		$ 367,353

Number of shares cancelled.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The total accumulated difference between fair values of underlying shares on dates of exercise and exercise price on options which were exercised (or share units converted) into shares during the reporting period under the plan.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Gross number of share options (or share units) granted during the period.

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The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance sheet date, including vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise prices of fully vested and expected to vest options outstanding.

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As of the balance sheet date, the number of shares into which fully vested and expected to vest stock options outstanding can be converted under the option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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