Shareholders' Equity - Summary of Activities in Common Stock (Detail) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Equity [Abstract]
Stock option exercises, Shares	79	180
Employee stock plan purchases, Shares	8	10
Purchase of common stock, Shares	(758)
Stock option exercises, Amount	$ 1,781	$ 3,425
Employee stock plan purchases, Amount	1,238	$ 900
Purchase of common stock	$ (94,497)