Fair Value of Financial Instruments - Schedule of Fair Value of Financial Assets and Liabilities (Detail) - USD ($) | Jun. 30, 2015 | Dec. 31, 2014 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of short and long term investments | $ 77,933,000 | $ 0 |
Commercial Paper [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of short and long term investments | 12,982,000 | |
Corporate Bonds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of short and long term investments | 57,947,000 | |
US Government Agency Obligations [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of short and long term investments | 7,004,000 | |
Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of financial assets | 99,538,000 | 100,000,000 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of financial assets | 14,605,000 | 100,000,000 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of financial assets | 84,933,000 | 0 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of financial assets | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of cash and cash equivalents | 14,605,000 | 100,000,000 |
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of cash and cash equivalents | 14,605,000 | 100,000,000 |
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of cash and cash equivalents | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of cash and cash equivalents | 0 | $ 0 |
Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of cash and cash equivalents | 15,982,000 | |
Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of cash and cash equivalents | 0 | |
Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of cash and cash equivalents | 15,982,000 | |
Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of cash and cash equivalents | 0 | |
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of short and long term investments | 61,947,000 | |
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of short and long term investments | 0 | |
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of short and long term investments | 61,947,000 | |
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of short and long term investments | 0 | |
Fair Value, Measurements, Recurring [Member] | US Government Agency Obligations [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of short and long term investments | 7,004,000 | |
Fair Value, Measurements, Recurring [Member] | US Government Agency Obligations [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of short and long term investments | 0 | |
Fair Value, Measurements, Recurring [Member] | US Government Agency Obligations [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of short and long term investments | 7,004,000 | |
Fair Value, Measurements, Recurring [Member] | US Government Agency Obligations [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair value of short and long term investments | $ 0 | |