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Nature of Business and Basis of Presentation - Additional Information (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Jun. 30, 2015
Dec. 31, 2014
Jun. 30, 2014
Dec. 31, 2013
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]        
Cash and cash equivalents $ 136,050 $ 119,539 $ 150,528 $ 191,514
Convertible Debt | 2012 Notes        
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]        
Convertible senior notes, earliest redemption date Jan. 19, 2017      
Convertible Debt | 2014 Notes        
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]        
Convertible senior notes, earliest redemption date Jan. 19, 2019