Unaudited Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net Income (loss)		$ 15,055	$ (3,305)	$ 43,158	$ 3,752
Other comprehensive income (loss):
Unrealized changes in fair value of interest rate swaps, net of income taxes	[1]	112	55	343	34
Foreign currency translation adjustments		589	713	764	888
Unrealized holding gains on available-for-sale investments arising during the period, net of income taxes	[2],[3]		534		717
Realized gains on available-for-sale investments reclassified into income, net of taxes	[2],[4]		(387)		(571)
Total other comprehensive income (loss)		701	915	1,107	1,068
Total comprehensive income (loss)		$ 15,756	$ (2,390)	$ 44,265	$ 4,820

[1] Net of income taxes of $17, ($5), $107 and ($18), respectively.

[2] In accordance with the adoption of ASU 2016-01 on January 1, 2018 (see Note 4), unrealized holding gains and losses on equity securities have been reclassified to income for the current period and to retained earnings for historical amounts recorded in Accumulated Other Comprehensive Income at December 31, 2017.

[3] Net of income taxes of $0, $312, $0 and $423, respectively.

[4] Net of income taxes of $0, $231, $0 and $352, respectively.