Convertible Notes (Summary of Series 2012 Notes) (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Feb. 17, 2015	Dec. 31, 2014	Oct. 20, 2014	Feb. 12, 2014	Feb. 06, 2014	Aug. 01, 2013
Debt Instrument [Line Items]
Convertible Notes Payable, Carrying Value	$ 232,443	$ 253,828		$ 444,771
Series 2012 Notes [Member]
Debt Instrument [Line Items]
Convertible Notes, Principal Balance Outstanding			$ 22,300		$ 22,300		$ 48,300	$ 180,000
Unamortized discount of liability component					$ (100)	$ (2,100)
Convertible Notes Payable, Carrying Value	$ 0	$ 0		$ 22,261