Stockholders' Equity and Employee Benefit Plans - Additional Information (Details) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended		12 Months Ended			19 Months Ended
	Aug. 21, 2015 USD ($) $ / shares shares	Feb. 28, 2019 shares	Mar. 31, 2018 shares	Jun. 30, 2017 shares	Dec. 31, 2018 USD ($) offering_period $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	May 31, 2015 $ / shares shares	Sep. 05, 2018 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted		2,225,766			5,735,643	4,139,372	5,014,600	16,700,000
Stock options granted, price per share | $ / shares					$ 13.31	$ 16.03	$ 16.03	$ 42.33
Stock-based compensation expense | $	$ 19,800				$ 84,989
Recognized service period of new award	4 years
Unrecognized compensation expense relating to repriced and exchanged awards | $					1,100
August 2015 Modification
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted	6,000,000
Stock options granted, price per share | $ / shares	$ 16.03
Stock options exchanged	11,900,000
Unrecognized share-based compensation expense, recognition end year	2019
2016 Modification | General and Administrative and Restructuring Costs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock awards							100,000
Stock options							900,000
Stock-based compensation expense | $							$ 2,500
Second Quarter 2017 Modification | Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock awards				500,000
Stock-based compensation expense | $						$ (1,100)
First Quarter 2018 Modification | Research and Development and Sales and Marketing Costs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock awards			500,000
Stock-based compensation expense | $					$ (500)
Common Stock | August 2015 Modification
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of common stock | $ / shares	$ 14.38
Out-of-the-Money Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value assumptions, method used					Lattice-Binomial Option Valuation Model
At-the-Money Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value assumptions, method used					Black-Scholes-Merton Valuation Model
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense | $					$ 45,217
Stock Options | 2016 Modification | General and Administrative and Restructuring Costs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense | $							1,400
Restricted Stock Units | 2016 Modification | General and Administrative and Restructuring Costs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense | $							$ 1,100
Maximum | Out-of-the-Money Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of common stock | $ / shares						$ 12.33	$ 12.28
Maximum | At-the-Money Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of common stock | $ / shares					$ 13.65
Minimum | Out-of-the-Money Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of common stock | $ / shares						$ 11.84	$ 12.21
Minimum | At-the-Money Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of common stock | $ / shares					$ 12.00
2018 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares reserved									9,394,744
2018 Equity Incentive Plan | Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant					13,626,822
2018 Equity Incentive Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual increases in number of shares available for issuance									12,500,000
Percentage of outstanding shares									5.00%
Equity Incentive Plans | Time-Based Awards | New Hires
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period					4 years
Equity Incentive Plans | Time-Based Awards | Existing Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period					3 years
Equity Incentive Plans | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period					10 years
2018 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares reserved									2,673,444
Offering period					24 months
Number of offering periods | offering_period					4
Length of purchase period					6 months
Employee share purchase price percentage					85.00%
Initial offering period start date					Sep. 25, 2018
Initial offering period end date					Nov. 22, 2020
Fair value of common stock | $ / shares					$ 12.89
2018 Employee Stock Purchase Plan | Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant					2,673,444
2018 Employee Stock Purchase Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual increases in number of shares available for issuance									5,346,888
Percentage of outstanding shares									1.00%