Fair Value Measurements - Financial Assets and Liabilities Carried at Fair Value (Detail) (USD $) | Jun. 28, 2014 | Dec. 31, 2013 |
In Thousands, unless otherwise specified |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | $458,232 | $352,968 |
Total assets at fair value | 464,117 | 357,795 |
Total liabilities at fair value | 3,051 | 7,570 |
U.S. Government and Agency Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 161,471 | 89,626 |
Forward Contracts [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Total assets at fair value | 401 | ' |
Total liabilities at fair value | ' | 2,743 |
Forward interest rate swap contracts [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Total liabilities at fair value | -2,433 | ' |
Level 1 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 161,471 | 89,626 |
Total assets at fair value | 167,462 | 94,453 |
Total liabilities at fair value | 5,484 | 5,992 |
Level 1 [Member] | U.S. Government and Agency Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 161,471 | 89,626 |
Level 1 [Member] | Forward Contracts [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Total assets at fair value | 507 | ' |
Total liabilities at fair value | ' | 1,165 |
Level 1 [Member] | Forward interest rate swap contracts [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Total liabilities at fair value | 0 | ' |
Level 2 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 294,173 | 260,754 |
Total assets at fair value | 294,067 | 260,754 |
Total liabilities at fair value | -2,433 | 1,578 |
Level 2 [Member] | U.S. Government and Agency Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 0 | 0 |
Level 2 [Member] | Forward Contracts [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Total assets at fair value | -106 | ' |
Total liabilities at fair value | ' | 1,578 |
Level 2 [Member] | Forward interest rate swap contracts [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Total liabilities at fair value | -2,433 | ' |
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 and Agency Securities [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] | Forward interest rate swap contracts [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Total liabilities at fair value | 0 | ' |
Other Investments [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 21,246 | 11,785 |
Other Investments [Member] | Level 1 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 0 | 0 |
Other Investments [Member] | Level 2 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 21,246 | 11,785 |
Other Investments [Member] | Level 3 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 0 | 0 |
Obligations of Government-Sponsored Enterprises [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 27,298 | 33,510 |
Obligations of Government-Sponsored Enterprises [Member] | Level 1 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 0 | 0 |
Obligations of Government-Sponsored Enterprises [Member] | Level 2 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 27,298 | 33,510 |
Obligations of Government-Sponsored Enterprises [Member] | Level 3 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 0 | 0 |
State and Municipal Bonds [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 53,858 | 51,627 |
State and Municipal Bonds [Member] | Level 1 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 0 | 0 |
State and Municipal Bonds [Member] | Level 2 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 53,858 | 51,627 |
State and Municipal Bonds [Member] | Level 3 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 0 | 0 |
Corporate Securities [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 194,359 | 166,420 |
Corporate Securities [Member] | Level 1 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 0 | 0 |
Corporate Securities [Member] | Level 2 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 191,771 | 163,832 |
Corporate Securities [Member] | Level 3 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Investments subtotal | 2,588 | 2,588 |
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 | 5,484 | 4,827 |
Money Market Investments Related to the Deferred Compensation Plan [Member] | Level 1 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Total assets at fair value | 5,484 | 4,827 |
Money Market Investments Related to the Deferred Compensation Plan [Member] | Level 2 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Total assets at fair value | 0 | 0 |
Money Market Investments Related to the Deferred Compensation Plan [Member] | Level 3 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Total assets at fair value | 0 | 0 |
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 | 5,484 | 4,827 |
Liabilities Related to the Deferred Compensation Plan [Member] | Level 1 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Total liabilities at fair value | 5,484 | 4,827 |
Liabilities Related to the Deferred Compensation Plan [Member] | Level 2 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Total liabilities at fair value | 0 | 0 |
Liabilities Related to the Deferred Compensation Plan [Member] | Level 3 [Member] | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Total liabilities at fair value | $0 | $0 |