Fair Value of Financial Instruments Financial Instruments Measured at Fair Value on Recurring Basis by Level within Fair Value Hierarchy (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Financial Assets
Marketable securities	$ 82,648,000	$ 112,544,000
Financial Liabilities
Financial liability	3,680,000	5,914,000
Warrant liability	0	688,000
Fair Value, Measurements, Recurring
Financial Assets
Cash equivalents	10,431,000	21,552,000
Marketable securities	82,648,000	112,544,000
Financial Assets Total	93,079,000	134,096,000
Financial Liabilities
Financial liability	3,680,000	5,914,000
Warrant liability	0	688,000
Financial Liabilities Total	3,680,000	6,602,000
Fair Value, Measurements, Nonrecurring
Financial Liabilities
Financial Liabilities Total		0
Level 1 | Fair Value, Measurements, Recurring
Financial Assets
Cash equivalents	3,720,000	15,683,000
Marketable securities	1,800,000	0
Financial Assets Total	5,520,000	15,683,000
Financial Liabilities
Financial liability	0	0
Warrant liability	0	0
Financial Liabilities Total	0	0
Level 2 | Fair Value, Measurements, Recurring
Financial Assets
Cash equivalents	6,711,000	5,869,000
Marketable securities	80,848,000	112,544,000
Financial Assets Total	87,559,000	118,413,000
Financial Liabilities
Financial liability	0	0
Warrant liability	0	0
Financial Liabilities Total	0	0
Level 3 | Fair Value, Measurements, Recurring
Financial Assets
Cash equivalents	0	0
Marketable securities	0	0
Financial Assets Total	0	0
Financial Liabilities
Financial liability	3,680,000	5,914,000
Warrant liability	0	688,000
Financial Liabilities Total	$ 3,680,000	$ 6,602,000