Stockholders' Equity - Schedule of Reserved Shares of Common Stock (Details) - shares	Mar. 31, 2019	Dec. 31, 2018
Stock-based compensation
Reserved shares of common stock	21,688,569	19,455,414
Stock options
Stock-based compensation
Reserved shares of common stock	6,156,932	6,329,737
RSUs
Stock-based compensation
Reserved shares of common stock	1,845,000	1,845,000
Shares available for future grant
Stock-based compensation
Reserved shares of common stock	13,686,637	11,280,677