Convertible Notes (Summary of Series 2012 Notes) (Detail) (USD $)	Jun. 30, 2013	Dec. 31, 2012	Jan. 31, 2012
Debt Instrument [Line Items]
Convertible Notes Payable, Carrying Value	$ 315,320,000	$ 309,952,000
Series 2012 Notes [Member]
Debt Instrument [Line Items]
Convertible Notes, Principal Balance Outstanding	179,000,000	179,000,000
Unamortized discount of liability component	(10,472,000)	(13,472,000)	(2,300,000)
Convertible Notes Payable, Carrying Value	$ 168,528,000	$ 165,528,000