Employee Savings Plan and Employee Stock Purchase Plan - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Contribution Plan Disclosure [Line Items]
401(k) eligible age of employee			18 years
401(k) eligibility minimum service period			90 days
Employee vested percentage in salary deferrals and roll over contributions			100.00%
Minimum period for vesting 100% contributions			2 years
Minimum period for vesting of discretionary contributions			2 years
Matching contribution	$ 1,900,000	$ 1,500,000	$ 6,300,000	$ 4,800,000
Employee stock purchase plan overlapping offering period			24 months
Employee Stock Purchase Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Employees Company's common stock shares purchase limit percentage	10.00%		10.00%
Employees Company's common stock shares purchase limit amount			$ 25,000
Purchase price of common stock expressed as a percentage of its fair market value			85.00%
Maximum number of shares that may be purchased by a participant			2,000
Share of common stock purchase maximum			2,000,000.0
Purchase of shares of common stock			42,966	39,137
Compensation expense related to ESPP	$ 700,000	$ 400,000	$ 1,500,000	$ 1,300,000
After Two Years Of Employment [Member]
Defined Contribution Plan Disclosure [Line Items]
Matching contributions, vesting percentage			100.00%
One Hundred Percent Match For Percent Of Participants Contribution [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contribution percentage			100.00%
Percentage of salary deferrals			1.00%
50% Matching Contribution [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer contribution percentage			50.00%
Minimum [Member] | 50% Matching Contribution [Member]
Defined Contribution Plan Disclosure [Line Items]
Percentage of salary deferrals			2.00%
Maximum [Member]
Defined Contribution Plan Disclosure [Line Items]
Percentage of salary deferrals			3.50%
Maximum [Member] | 50% Matching Contribution [Member]
Defined Contribution Plan Disclosure [Line Items]
Percentage of salary deferrals			6.00%