401(k) Plan - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Contribution Plan Disclosure [Line Items]
Company's contribution to the plan, percentage	50.00%
Company's contribution to the plan, amount	$ 1,100,000	$ 900,000	$ 900,000
Company's matching contributions vesting annually	25.00%
Company's matching contributions vesting after four consecutive years of service	100.00%
Vesting period identified for vesting purpose	4 years
Maximum [Member]
Defined Contribution Plan Disclosure [Line Items]
Annual contribution by employer	$ 3,000	$ 2,000	$ 2,000