Fair Value Measurements (Summary Of Valuation Of Company's Financial Instruments By Various Levels) (Details) - USD ($) $ in Thousands		Oct. 01, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value		$ 143,858	$ 151,304
Liabilities, Fair value		11,749	1,705
Quoted Market Prices In Active Markets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value		141,318	142,541
Liabilities, Fair value		0	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value		2,540	8,763
Liabilities, Fair value		11,749	1,705
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value		0	0
Liabilities, Fair value		0	0
Foreign Currency Forward Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value	[1]	2,540	8,763
Liabilities, Fair value	[2]	11,749	1,705
Foreign Currency Forward Contracts [Member] | Quoted Market Prices In Active Markets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value	[1]	0	0
Liabilities, Fair value	[2]	0	0
Foreign Currency Forward Contracts [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value	[1]	2,540	8,763
Liabilities, Fair value	[2]	11,749	1,705
Foreign Currency Forward Contracts [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value	[1]	0	0
Liabilities, Fair value	[2]	0	0
Money Market Funds [Member] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value		15,105	17,027
Money Market Funds [Member] | Cash Equivalents [Member] | Quoted Market Prices In Active Markets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value		15,105	17,027
Money Market Funds [Member] | Cash Equivalents [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value		0	0
Money Market Funds [Member] | Cash Equivalents [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value		0	0
U.S. Treasuries [Member] | Available-For-Sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value	[3]	124,087	123,838
U.S. Treasuries [Member] | Available-For-Sale Securities [Member] | Quoted Market Prices In Active Markets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value	[3]	124,087	123,838
U.S. Treasuries [Member] | Available-For-Sale Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value	[3]	0	0
U.S. Treasuries [Member] | Available-For-Sale Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value	[3]	0	0
Certificates Of Deposits [Member] | Available-For-Sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value	[3]	162	148
Certificates Of Deposits [Member] | Available-For-Sale Securities [Member] | Quoted Market Prices In Active Markets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value	[3]	162	148
Certificates Of Deposits [Member] | Available-For-Sale Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value	[3]	0	0
Certificates Of Deposits [Member] | Available-For-Sale Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value	[3]	0	0
Mutual Funds [Member] | Trading Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value	[3]	1,964	1,528
Mutual Funds [Member] | Trading Securities [Member] | Quoted Market Prices In Active Markets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value	[3]	1,964	1,528
Mutual Funds [Member] | Trading Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value	[3]	0	0
Mutual Funds [Member] | Trading Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair value	[3]	$ 0	$ 0

[1] Included in prepaid expenses and other current assets on the Company’s unaudited condensed consolidated balance sheets.

[2] Included in other accrued liabilities on the Company’s unaudited condensed consolidated balance sheets.

[3] Included in short-term investments on the Company’s unaudited condensed consolidated balance sheets.