Financial Instruments Measured at Fair Value on Recurring Basis by Level within Fair Value Hierarchy (Detail) (USD $)	Dec. 31, 2013	Jan. 24, 2013	Dec. 31, 2012
Financial Assets
Marketable securities	$ 112,544,000		$ 118,187,000
Financial Liabilities
Derivative liability	5,914,000	3,124,000
Warrant liability	688,000		835,000
Fair Value, Measurements, Recurring [Member]
Financial Assets
Cash equivalents	21,552,000		28,610,000
Marketable securities	112,544,000		118,187,000
Financial Assets Total	134,096,000		146,797,000
Financial Liabilities
Derivative liability	5,914,000
Warrant liability	688,000		835,000
Financial Liabilities Total	6,602,000
Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Financial Assets
Cash equivalents	15,683,000		25,781,000
Marketable securities			1,997,000
Financial Assets Total	15,683,000		27,778,000
Financial Liabilities
Derivative liability
Warrant liability
Financial Liabilities Total
Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Financial Assets
Cash equivalents	5,869,000		2,829,000
Marketable securities	112,544,000		116,190,000
Financial Assets Total	118,413,000		119,019,000
Financial Liabilities
Derivative liability
Warrant liability
Financial Liabilities Total
Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Financial Assets
Cash equivalents
Marketable securities
Financial Assets Total
Financial Liabilities
Derivative liability	5,914,000
Warrant liability	688,000		835,000
Financial Liabilities Total	$ 6,602,000