Share-Based Compensation - Schedule of Restricted Stock Units to be Settled in Cash (Detail) shares in Thousands	9 Months Ended
	Sep. 30, 2018 shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Beginning balance of Outstanding, Restricted Stock Units to be Settled in Cash	472
Restricted Stock Units to be Settled in Cash, Vested	(210)
Restricted Stock Units to be Settled in Cash, Forfeited	(45)
Ending balance of Outstanding, Restricted Stock Units to be Settled in Cash	217