Fair Value Measurements - Schedule of Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	$ 90,659	$ 166,038
Total liabilities measured at fair value	0	0
Level 1 | U.S. government agency obligations
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	0
Level 1 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	90,659	166,038
Level 1 | Derivative liabilities associated with the Medicis settlement
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total liabilities measured at fair value	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	52,936	0
Total liabilities measured at fair value	0	0
Level 2 | U.S. government agency obligations
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	52,936
Level 2 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	0	0
Level 2 | Derivative liabilities associated with the Medicis settlement
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total liabilities measured at fair value	0	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	0	0
Total liabilities measured at fair value	1,494	1,541
Level 3 | U.S. government agency obligations
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	0
Level 3 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	0	0
Level 3 | Derivative liabilities associated with the Medicis settlement
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total liabilities measured at fair value	1,494	1,541
Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	143,595	166,038
Total liabilities measured at fair value	1,494	1,541
Recurring | U.S. government agency obligations
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	52,936
Recurring | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	90,659	166,038
Recurring | Derivative liabilities associated with the Medicis settlement
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total liabilities measured at fair value	$ 1,494	$ 1,541