Earnings Per Share (Calculation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2018	Sep. 29, 2017	Sep. 28, 2018	Sep. 29, 2017
Earnings Per Share [Abstract]
Net income attributable to FOX stockholders	$ 24,312	$ 16,072	$ 63,906	$ 40,326
Weighted average shares used to compute basic earnings per share (in shares)	37,886	37,474	37,743	37,312
Dilutive effect of employee stock plans (in shares)	1,166	1,343	1,170	1,388
Weighted average shares used to compute diluted earnings per share (in shares)	39,052	38,817	38,913	38,700
Basic (in dollars per share)	$ 0.64	$ 0.43	$ 1.69	$ 1.08
Diluted (in dollars per share)	$ 0.62	$ 0.41	$ 1.64	$ 1.04