Fair Value Measurements (Financial Assets And Liabilities Carried At Fair Value) (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	$ 281,454		$ 290,277
Total assets at fair value	293,861		302,686
Total liabilities at fair value	3,088		3,199
US Government Corporations and Agencies Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	63,802		50,847
Obligations Of Government And Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	12,241	[1]	16,612	[1]
State And Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	103,869		142,873
Corporate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	101,506		79,909
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	9,319	[2]	9,210	[2]
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	3,088		3,199
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	3,088		3,199
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	41,915		25,540
Total assets at fair value	48,454		31,365
Total liabilities at fair value	3,088		3,199
Fair Value, Inputs, Level 1 [Member] | US Government Corporations and Agencies Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	41,915		25,540
Fair Value, Inputs, Level 1 [Member] | Obligations Of Government And Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	0	[1]	0	[1]
Fair Value, Inputs, 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
Fair Value, Inputs, Level 1 [Member] | Corporate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	0		0
Fair Value, Inputs, Level 1 [Member] | Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	0		0
Fair Value, Inputs, Level 1 [Member] | Forward Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	3,451	[2]	2,626	[2]
Fair Value, Inputs, 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	3,088		3,199
Fair Value, Inputs, 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	3,088		3,199
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	236,951		262,149
Total assets at fair value	242,819		268,733
Total liabilities at fair value	0		0
Fair Value, Inputs, Level 2 [Member] | US Government Corporations and Agencies Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	21,887		25,307
Fair Value, Inputs, Level 2 [Member] | Obligations Of Government And Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	12,241	[1]	16,612	[1]
Fair Value, Inputs, Level 2 [Member] | State And Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	103,869		142,873
Fair Value, Inputs, Level 2 [Member] | Corporate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	98,918		77,321
Fair Value, Inputs, Level 2 [Member] | Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	36		36
Fair Value, Inputs, Level 2 [Member] | Forward Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	5,868	[2]	6,584	[2]
Fair Value, Inputs, 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
Fair Value, Inputs, 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
Fair Value, Inputs, 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
Fair Value, Inputs, Level 3 [Member] | US Government Corporations and Agencies Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	0		0
Fair Value, Inputs, Level 3 [Member] | Obligations Of Government And Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	0	[1]	0	[1]
Fair Value, Inputs, 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
Fair Value, Inputs, 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
Fair Value, Inputs, Level 3 [Member] | Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments subtotal	0		0
Fair Value, Inputs, 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	[2]	0	[2]
Fair Value, Inputs, 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
Fair Value, Inputs, 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

[1] Includes investments in notes issued by the Federal Home Loan Mortgage Corporation, the Federal National Mortgage Association, the Federal Farm Credit Banks and the Federal Home Loan Bank.

[2] The fair value of forward contracts are calculated as follows: a. Fair value of forward collar contract associated with forecasted sales hedges are calculated using the midpoint of ask and bid rates for similar contracts. b. Fair value of regular forward contracts associated with forecasted sales hedges are calculated using the period-end exchange rate adjusted for the discount rate (3 month LIBOR rate). c. Fair value of balance sheet hedges are calculated at the period end exchange rate adjusted for current forward points unless the hedge has been traded but not settled at period end. If this is the case, the fair value is calculated at the rate at which the hedge is being settled.