Shareholders' Equity - Summary of Activities in Common Stock (Detail) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Equity [Abstract]
Purchases of common stock (in shares)	0	0	(72)	0
Stock option exercises (in shares)	203	372	297	722
Employee stock plan purchases (in shares)	13	11	28	23
Restricted stock units vested, net of withheld shares upon award settlement (in shares)	27	0	37	0
Purchases of treasury shares	$ 0	$ 0	$ (14,289)	$ 0
Stock option exercises	15,604	25,019	22,132	44,317
Employee stock plan purchases	2,260	1,962	4,609	3,760
Restricted stock units vested, net of withheld shares upon award settlement	$ (2,008)	$ 0	$ (3,381)	$ 0