Fair Value of All Employee Stock Options (Detail) (Employee Stock Option)	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Method Used [Line Items]
Weighted-average expected term (years)	6 years 6 months 18 days	6 years 8 months 16 days
Weighted-average volatility	76.00%	71.00%
Risk-free interest rate	1.08%	1.81%
Expected dividends	0.00%	0.00%

The range of expected volatilities used and the weighted-average expected volatility for an entity using a valuation technique with different volatilities during the contractual term.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (f)(2)(ii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph e(2)(b)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration