Consolidated Statement of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity
Adjustment as a result of the adoption of ASU 2016-16 Income Taxes - Intra-Entity Transfers Other than Inventory (Note 12)	$ (5,961)			$ (5,961)
Beginning Balance, Shares at Dec. 31, 2017	173,507	173,507
Beginning Balance at Dec. 31, 2017	$ 1,095,673	$ 347	$ 461,338	668,587	$ (34,599)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under stock plans, shares		697
Issuance of common stock under stock plans	11,123	$ 1	11,122
Repurchase of common stock (in shares)		(1,256)
Repurchase of common stock	(69,202)	$ (2)		(69,200)
Stock-based compensation expense	13,194		13,194
Payment of dividends	(7,787)			(7,787)
Net income	37,217			37,217
Net unrealized gain (loss) on available-for-sale investments, net of tax of ($114)	(1,192)				(1,192)
Reclassification of net realized (gain) loss on the sale of available-for-sale investments	(22)				(22)
Foreign currency translation adjustment	$ 4,056				4,056
Ending Balance, Shares at Apr. 01, 2018	172,948	172,948
Ending Balance at Apr. 01, 2018	$ 1,077,099	$ 346	$ 485,654	$ 622,856	$ (31,757)