Fair Value of Financial Instruments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities with an original maturity	greater than three months
Fair Value [Member] | Level 3 [Member] | Hercules [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes	$ 40.2
Carrying Value [Member] | Level 3 [Member] | Hercules [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes	40.4
Senior Convertible Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Principal amount	125.0
Senior Convertible Notes [Member] | Fair Value [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes	126.4
Senior Convertible Notes [Member] | Carrying Value [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes	$ 74.6
Maximum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liquid investments with an original maturity	3 months