Defined Contribution Plan - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018
Defined Contribution Plan Disclosure [Line Items]
Employer matching contribution, percent of employees' gross pay	4.00%
Defined Contribution Plan, Tax Status [Extensible List]	us-gaap:QualifiedPlanMember
Maximum [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer's matching contribution percentage	50.00%