Stock-Based Compensation - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2018
Non-Performance Based Grants | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment award, award vesting period	3 years
Non-Performance Based Grants | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment award, award vesting period	4 years
Performance Based Grants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based payment award, award vesting period	3 years