Fair Value Measurements - Summary of Warrant Liabilities Measured at Fair Value on a Recurring Basis Using Unobservable Inputs (Detail) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2015 |
Jun. 30, 2014 |
Jun. 30, 2015 |
Jun. 30, 2014 |
|
| Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] | ||||
| Fair value of preferred stock warrants exercised | $ 1,100 | |||
| Change in fair value of preferred stock warrants | $ 8,630 | $ 347 | 9,956 | $ 496 |
| Level 3 [Member] | ||||
| Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] | ||||
| Balance as of December 31, 2014 | 1,810 | |||
| Fair value of preferred stock warrants exercised | (1,125) | |||
| Change in fair value of preferred stock warrants | 9,956 | |||
| Balance as of June 30, 2015 | $ 10,641 | $ 10,641 | ||