Stockholders' Equity (Detail)				12 Months Ended
	Jun. 17, 2020 shares	Jun. 26, 2018 shares	Apr. 03, 2018 shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares
Class of Stock [Line Items]
Stock issued during period subject to lock-up and stand-still provisions period			5 years
Number of shares to be issued upon exercise of outstanding options or vesting of RSUs				20,894,000
Common stock, shares authorized (in shares)				300,000,000	300,000,000
Maximum 401(k) per employee, percentage of annual salary				60.00%
Matching 401(k) employer contribution, maximum amount | $				$ 6,000
Compensation expense in connection with 401(k) retirement plan | $				$ 3,500,000	$ 3,500,000	$ 2,800,000
Change in control severance payment period for executives				12 months
Change in control severance payment period for Chief Executive Officer				24 months
Change in control severance payment period for senior vice presidents and vice presidents				12 months
Change in control severance payment period for employees				6 months
Employee Stock Purchase Plan
Class of Stock [Line Items]
Common stock, shares authorized (in shares)				2,500,000
Percentage of purchase price of stock				85.00%
Employee Stock Purchase Plan
Class of Stock [Line Items]
Increase in aggregate number of shares authorized (in shares)	1,000,000
2017 Performance Incentive Plan
Class of Stock [Line Items]
Number of shares available for issuance under equity compensation plans				7,569,000
Number of common stock shares available for stock options grants				8,300,000
Number of additional shares available for award grants		10,900,000
Share-based compensation plan's share limit reduction for every one restricted stock unit granted (in shares)				1.5
Stock options term under equity incentive plans				8 years
Employee Stock Purchase Plan
Class of Stock [Line Items]
Number of shares available for issuance under equity compensation plans				1,321,000
Amended and Restated 2017 Plan
Class of Stock [Line Items]
Increase in aggregate number of shares authorized (in shares)	10,000,000
Common Stock
Class of Stock [Line Items]
Sale of common stock (in shares)			8,284,600			8,285,000
Common stock, shares reserved for issuance in equity compensation plans				29,784,000
Employee | 2017 Performance Incentive Plan | Shares of Common Stock Underlying Outstanding Stock Options
Class of Stock [Line Items]
Service period for stock-based compensation award granted				4 years
Employee | 2017 Performance Incentive Plan | RSUs and PSUs
Class of Stock [Line Items]
Service period for stock-based compensation award granted				3 years
Director | 2017 Performance Incentive Plan | Shares of Common Stock Underlying Outstanding Stock Options
Class of Stock [Line Items]
Service period for stock-based compensation award granted				1 year
Director | 2017 Performance Incentive Plan | RSUs and PSUs
Class of Stock [Line Items]
Service period for stock-based compensation award granted				1 year