Stock-Based Compensation - Additional Information (Detail) (USD $)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum shares of common stock authorized for issuance and available for future grants	90,000,000
Purchase of common stock	63,847,938
Shares of common stock available for future grants	26,152,062
Weighted average fair value of options granted	$ 0.07
Forfeiture rate for options granted to employees	5.00%
Forfeiture rate for options granted to directors	0.00%
Weighted-average remaining contractual life of options outstanding	9 years 4 months 24 days
Weighted-average remaining contractual life of options exercisable	9 years 4 months 21 days
Aggregate intrinsic value of options outstanding	$ 1,900
Aggregate intrinsic value of exercisable options	950
Stock-based compensation	114,000	(79,000)
Exercise price of options, Minimum	$ 0.65
Exercise price of options, Maximum	$ 7.50
Rxi [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	968,000	2,111,000
Unrecognized compensation cost	3,859,000
Predecessor [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase of common stock	477,191
Weighted average fair value of options granted	$ 0.47	$ 0.98
Forfeiture rate for options granted to employees	15.00%
Forfeiture rate for options granted to directors	0.00%
Stock-based compensation	$ 283,000	$ 2,111,000
Forfeiture rate for options granted to senior management	8.00%

Forfeiture rate for options granted to directors.

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Forfeiture rate for options granted to employees.

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Forfeiture rate for options granted to senior management.

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- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

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-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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- Definition

Aggregate unrecognized cost of option awards made to employees under a stock option plan or plans, that have yet to vest.

+ References

No definition available.

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- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

+ References

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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- Definition

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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- Definition

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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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

+ References

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

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

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- Definition

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.

+ References

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-Publisher FASB

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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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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- Definition

The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

+ References

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The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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