Fair Value of Financial Instruments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 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	$ 39.6
Carrying Value [Member] | Level 3 [Member] | Hercules [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes	40.5
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	170.2
Senior Convertible Notes [Member] | Carrying Value [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes	$ 76.6
Maximum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liquid investments with an original maturity	3 months