Financial Instruments Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Derivatives, Fair Value [Line Items]
Total cash and cash equivalents, Carrying Amount	$ 50,332	$ 114,094	$ 44,791	$ 108,172
Total, Carrying Amount	98,711	172,368
Warrant Liabilities	2,935
Total, Estimated Fair Value	98,711	172,368
Cash and Cash Equivalents
Derivatives, Fair Value [Line Items]
Total cash and cash equivalents, Carrying Amount	50,332	114,094
Total cash and cash equivalents, Estimated Fair Value	50,332	114,094
Cash and Cash Equivalents | Cash
Derivatives, Fair Value [Line Items]
Total cash and cash equivalents, Carrying Amount	14,221	8,680
Total cash and cash equivalents, Estimated Fair Value	14,221	8,680
Cash and Cash Equivalents | Money market funds
Derivatives, Fair Value [Line Items]
Total cash and cash equivalents, Carrying Amount	36,111	105,414
Total cash and cash equivalents, Estimated Fair Value	36,111	105,414
Total short-term investments | Certificates of deposit
Derivatives, Fair Value [Line Items]
Total short-term investments, Carrying Amount	45,949	55,694
Total short-term investments, Estimated Fair Value	45,949	55,694
Restricted cash | Certificates of deposit
Derivatives, Fair Value [Line Items]
Total cash and cash equivalents, Carrying Amount	2,430	2,580
Total cash and cash equivalents, Estimated Fair Value	2,430	2,580
Embedded Derivative
Derivatives, Fair Value [Line Items]
Liabilities, Carrying Amount	3,783
Liabilities, Estimated Fair Value	3,783
Embedded Derivative | Debt Redemption Features
Derivatives, Fair Value [Line Items]
Total embedded derivatives, Carrying Amount	848
Total embedded derivatives, Estimated Fair Value	848
Embedded Derivative | Warrant Liability
Derivatives, Fair Value [Line Items]
Warrant Liabilities	2,935
Liabilities, Estimated Fair Value	2,935
Level 1
Derivatives, Fair Value [Line Items]
Total, Estimated Fair Value	98,711	172,368
Level 1 | Cash and Cash Equivalents
Derivatives, Fair Value [Line Items]
Total cash and cash equivalents, Estimated Fair Value	50,332	114,094
Level 1 | Cash and Cash Equivalents | Cash
Derivatives, Fair Value [Line Items]
Total cash and cash equivalents, Estimated Fair Value	14,221	8,680
Level 1 | Cash and Cash Equivalents | Money market funds
Derivatives, Fair Value [Line Items]
Total cash and cash equivalents, Estimated Fair Value	36,111	105,414
Level 1 | Total short-term investments | Certificates of deposit
Derivatives, Fair Value [Line Items]
Total short-term investments, Estimated Fair Value	45,949	55,694
Level 1 | Restricted cash | Certificates of deposit
Derivatives, Fair Value [Line Items]
Total cash and cash equivalents, Estimated Fair Value	2,430	2,580
Level 3 | Embedded Derivative
Derivatives, Fair Value [Line Items]
Liabilities, Estimated Fair Value	3,783
Level 3 | Embedded Derivative | Debt Redemption Features
Derivatives, Fair Value [Line Items]
Total embedded derivatives, Estimated Fair Value	848
Level 3 | Embedded Derivative | Warrant Liability
Derivatives, Fair Value [Line Items]
Liabilities, Estimated Fair Value	$ 2,935