Shareholders' Equity - Summary of Activities in Common Stock (Detail) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Equity [Abstract]
Purchases of common stock (in shares)	(72)	0
Stock option exercises (in shares)	94	350
Employee stock plan purchases (in shares)	15	12
Restricted stock units vested, net of withheld shares upon award settlement (in shares)	10	0
Treasury stock purchases	$ (14,289)	$ 0
Stock option exercises, amount	6,564	19,298
Issuance of shares pursuant to employee stock purchase plan	2,349	1,798
Restricted stock units vested, net of withheld shares upon award settlement	$ (1,373)	$ 0