Fair Value of Financial Instruments - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities with an original maturity	Greater than three months
Level 3 [Member] | Hercules [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt	$ 40,600,000
Carrying value of debt	40,500,000
Senior Convertible Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Principal amount	125,000,000
Carrying value of debt	78,600,000
Senior Convertible Notes [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt	$ 193,100,000
Maximum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liquid investments with an original maturity	3 months