Stock Based Compensation - Additional Information (Detail) shares in Millions	6 Months Ended
	Jun. 30, 2017 company shares
Growth Performance Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award performance period	2 years
Share-based Compensation Arrangement by Share-based Payment Award, Base Target Share Award | shares	0.1
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Cash Payout Ratio	100.00%
Growth Performance Stock Units | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights percentage	0.00%
Growth Performance Stock Units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rights percentage	250.00%
Performance Stock Unit awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Award performance period	3 years
Number of companies forming peer group | company	320
Percentage of award intended to pay out in stock	65.00%
Reserved percentage of award intended to pay out in cash	100.00%
Percentage recorded as a liability	35.00%
Performance Stock Unit awards | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Base award percentage of Total Shareholder Return	0.00%
Performance Stock Unit awards | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Base award percentage of Total Shareholder Return	175.00%