Financial Instruments Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010
Derivatives, Fair Value [Line Items]
Total cash and cash equivalents, Carrying Amount	$ 68,187	$ 114,094	$ 154,773	$ 44,791
Total cash and cash equivalents and short-term investments, Carrying Amount	48,054
Total, Carrying Amount	119,171	172,368
Warrant Liabilities	8,067
Liabilities, Carrying Amount	9,015
Total short-term investments, Estimated Fair Value		55,694
Total cash and cash equivalents and short-term investments, Estimated Fair Value	48,054
Total, Estimated Fair Value	119,171	172,368
Liabilities, Estimated Fair Value	9,015
Certificates of deposit
Derivatives, Fair Value [Line Items]
Total cash and cash equivalents, Carrying Amount		2,580
Total short-term investments, Carrying Amount		55,694
Total cash and cash equivalents and short-term investments, Carrying Amount	2,930
Total cash and cash equivalents, Estimated Fair Value	2,930	2,580
Restricted cash
Derivatives, Fair Value [Line Items]
Total cash and cash equivalents, Carrying Amount	2,930	2,580
Total cash and cash equivalents, Estimated Fair Value	2,930	2,580
Warrant Liability
Derivatives, Fair Value [Line Items]
Warrant Liabilities	8,067
Liabilities, Estimated Fair Value	8,067
Cash and Cash Equivalents
Derivatives, Fair Value [Line Items]
Total cash and cash equivalents, Carrying Amount	68,187	114,094
Total cash and cash equivalents, Estimated Fair Value	68,187	114,094
Cash and Cash Equivalents | Cash
Derivatives, Fair Value [Line Items]
Total cash and cash equivalents, Carrying Amount	22,275	8,680
Total cash and cash equivalents, Estimated Fair Value	22,275	8,680
Cash and Cash Equivalents | Money market funds
Derivatives, Fair Value [Line Items]
Total cash and cash equivalents, Carrying Amount	45,912	105,414
Total cash and cash equivalents, Estimated Fair Value	45,912	105,414
Total short-term investments
Derivatives, Fair Value [Line Items]
Total short-term investments, Carrying Amount		55,694
Total short-term investments, Estimated Fair Value		55,694
Total short-term investments | Certificates of deposit
Derivatives, Fair Value [Line Items]
Total short-term investments, Carrying Amount	48,054
Total short-term investments, Estimated Fair Value	48,054
Embedded Derivative
Derivatives, Fair Value [Line Items]
Total embedded derivatives, Carrying Amount	948
Total embedded derivatives, Estimated Fair Value	948
Embedded Derivative | Debt Redemption Features
Derivatives, Fair Value [Line Items]
Total embedded derivatives, Carrying Amount	948
Total embedded derivatives, Estimated Fair Value	948
Level 1
Derivatives, Fair Value [Line Items]
Total short-term investments, Estimated Fair Value		55,694
Total cash and cash equivalents and short-term investments, Estimated Fair Value	48,054
Total, Estimated Fair Value	119,171	172,368
Level 1 | Certificates of deposit
Derivatives, Fair Value [Line Items]
Total cash and cash equivalents, Estimated Fair Value	2,930	2,580
Level 1 | Restricted cash
Derivatives, Fair Value [Line Items]
Total cash and cash equivalents, Estimated Fair Value	2,930	2,580
Level 1 | Cash and Cash Equivalents
Derivatives, Fair Value [Line Items]
Total cash and cash equivalents, Estimated Fair Value	68,187	114,094
Level 1 | Cash and Cash Equivalents | Cash
Derivatives, Fair Value [Line Items]
Total cash and cash equivalents, Estimated Fair Value	22,275	8,680
Level 1 | Cash and Cash Equivalents | Money market funds
Derivatives, Fair Value [Line Items]
Total cash and cash equivalents, Estimated Fair Value	45,912	105,414
Level 1 | Total short-term investments
Derivatives, Fair Value [Line Items]
Total short-term investments, Estimated Fair Value		55,694
Level 1 | Total short-term investments | Certificates of deposit
Derivatives, Fair Value [Line Items]
Total short-term investments, Estimated Fair Value	48,054
Level 3
Derivatives, Fair Value [Line Items]
Liabilities, Estimated Fair Value	9,015
Level 3 | Warrant Liability
Derivatives, Fair Value [Line Items]
Liabilities, Estimated Fair Value	8,067
Level 3 | Embedded Derivative
Derivatives, Fair Value [Line Items]
Total embedded derivatives, Estimated Fair Value	948
Level 3 | Embedded Derivative | Debt Redemption Features
Derivatives, Fair Value [Line Items]
Total embedded derivatives, Estimated Fair Value	$ 948