Fair Value of Assets and Liabilities - Securities (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	Mar. 29, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities - mutual funds	$ 8,280	$ 7,351
Derivative contracts, net	(553)	(2,739)
Assets, fair value	155,340	144,814
U.S. Government-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	27,615	17,608
Agency bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	72,126	51,951
Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0	13,500
Certificates of deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	20,976	19,122
Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	16,140	27,119
Corporate Bond Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	10,756	10,902
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities - mutual funds	8,280	7,351
Derivative contracts, net	0	0
Assets, fair value	35,895	24,959
Fair Value, Inputs, Level 1 [Member] | U.S. Government-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	27,615	17,608
Fair Value, Inputs, Level 1 [Member] | Agency bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0	0
Fair Value, Inputs, Level 1 [Member] | Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0	0
Fair Value, Inputs, Level 1 [Member] | Certificates of deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0	0
Fair Value, Inputs, Level 1 [Member] | Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0	0
Fair Value, Inputs, Level 1 [Member] | Corporate Bond Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0	0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities - mutual funds	0	0
Derivative contracts, net	(553)	(2,739)
Assets, fair value	119,445	119,855
Fair Value, Inputs, Level 2 [Member] | U.S. Government-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0	0
Fair Value, Inputs, Level 2 [Member] | Agency bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	72,126	51,951
Fair Value, Inputs, Level 2 [Member] | Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0	13,500
Fair Value, Inputs, Level 2 [Member] | Certificates of deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	20,976	19,122
Fair Value, Inputs, Level 2 [Member] | Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	16,140	27,119
Fair Value, Inputs, Level 2 [Member] | Corporate Bond Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	10,756	10,902
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities - mutual funds	0	0
Derivative contracts, net	0	0
Assets, fair value	0	0
Fair Value, Inputs, Level 3 [Member] | U.S. Government-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0	0
Fair Value, Inputs, Level 3 [Member] | Agency bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0	0
Fair Value, Inputs, Level 3 [Member] | Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0	0
Fair Value, Inputs, Level 3 [Member] | Certificates of deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0	0
Fair Value, Inputs, Level 3 [Member] | Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	0	0
Fair Value, Inputs, Level 3 [Member] | Corporate Bond Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale marketable securities	$ 0	$ 0