Fair Value Measurements - Financial Assets and Liabilities Carried at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 30, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	$ 367,972	$ 329,335
Total assets at fair value	374,467	332,888
Total liabilities at fair value	3,917	5,598
U.S. Government Corporation and Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	104,862	96,987
Obligations of Government-Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	11,046	4,840
State and Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	111,559	96,516
Corporate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	140,469	130,956
Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	36	36
Forward Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	2,578
Total liabilities at fair value		2,045
Money Market Investments Related to the Deferred Compensation Plan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	3,917	3,553
Liabilities Related to the Deferred Compensation Plan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total liabilities at fair value	3,917	3,553
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	91,228	83,532
Total assets at fair value	96,720	87,085
Total liabilities at fair value	3,917	4,727
Level 1 [Member] | U.S. Government Corporation and Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	91,228	83,532
Level 1 [Member] | Obligations of Government-Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	0	0
Level 1 [Member] | State and Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	0	0
Level 1 [Member] | Corporate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	0	0
Level 1 [Member] | Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	0	0
Level 1 [Member] | Forward Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	1,575
Total liabilities at fair value		1,174
Level 1 [Member] | Money Market Investments Related to the Deferred Compensation Plan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	3,917	3,553
Level 1 [Member] | Liabilities Related to the Deferred Compensation Plan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total liabilities at fair value	3,917	3,553
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	274,156	243,215
Total assets at fair value	275,159	243,215
Total liabilities at fair value	0	871
Level 2 [Member] | U.S. Government Corporation and Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	13,634	13,455
Level 2 [Member] | Obligations of Government-Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	11,046	4,840
Level 2 [Member] | State and Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	111,559	96,516
Level 2 [Member] | Corporate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	137,881	128,368
Level 2 [Member] | Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	36	36
Level 2 [Member] | Forward Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	1,003
Total liabilities at fair value		871
Level 2 [Member] | Money Market Investments Related to the Deferred Compensation Plan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	0	0
Level 2 [Member] | Liabilities Related to the Deferred Compensation Plan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total liabilities at fair value	0	0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	2,588	2,588
Total assets at fair value	2,588	2,588
Total liabilities at fair value	0	0
Level 3 [Member] | U.S. Government Corporation and Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	0	0
Level 3 [Member] | Obligations of Government-Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	0	0
Level 3 [Member] | State and Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	0	0
Level 3 [Member] | Corporate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	2,588	2,588
Level 3 [Member] | Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	0	0
Level 3 [Member] | Forward Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	0
Total liabilities at fair value		0
Level 3 [Member] | Money Market Investments Related to the Deferred Compensation Plan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	0	0
Level 3 [Member] | Liabilities Related to the Deferred Compensation Plan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total liabilities at fair value	$ 0	$ 0