Stockholders' Equity - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Apr. 17, 2015	Nov. 06, 2013
Equity, Class of Treasury Stock [Line Items]
Share repurchase program authorized amount			$ 175,000,000	$ 125,000,000
Share repurchase program additional authorized amount			$ 50,000,000
Treasury stock value	$ 668,000	$ 8,359,000
Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Treasury stock shares acquired	0
Treasury stock available for repurchase	$ 70,800,000
Minimum tax withholding obligations
Equity, Class of Treasury Stock [Line Items]
Treasury stock shares acquired	17,000
Treasury stock value	$ 700,000