Fair Value Measurements (Financial Assets And Liabilities Carried At Fair Value) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	$ 320,301		$ 290,277
Total assets at fair value	323,804		302,686
Total liabilities at fair value	3,181		3,199
U.S. Government And Agency Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	56,829		50,847
Obligations Of Government-Sponsored Enterprises [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	14,944	[1]	16,612	[1]
State And Municipal Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	141,085		142,873
Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	107,407		79,909
Other Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	36		36
Money Market Investments Related To The Deferred Compensation Plan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets at fair value	3,181		3,199
Forward Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets at fair value	322	[2]	9,210	[2]
Liabilities Related To The Deferred Compensation Plan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total liabilities at fair value	3,181		3,199
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	32,486		25,540
Total assets at fair value	33,814		31,365
Total liabilities at fair value	3,181		3,199
Level 1 [Member] | U.S. Government And Agency Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	32,486		25,540
Level 1 [Member] | Obligations Of Government-Sponsored Enterprises [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	0	[1]	0	[1]
Level 1 [Member] | State And Municipal Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	0		0
Level 1 [Member] | Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	0		0
Level 1 [Member] | Other Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	0		0
Level 1 [Member] | Money Market Investments Related To The Deferred Compensation Plan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets at fair value	3,181		3,199
Level 1 [Member] | Forward Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets at fair value	(1,853)	[2]	2,626	[2]
Level 1 [Member] | Liabilities Related To The Deferred Compensation Plan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total liabilities at fair value	3,181		3,199
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	285,227		262,149
Total assets at fair value	287,402		268,733
Total liabilities at fair value	0		0
Level 2 [Member] | U.S. Government And Agency Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	24,343		25,307
Level 2 [Member] | Obligations Of Government-Sponsored Enterprises [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	14,944	[1]	16,612	[1]
Level 2 [Member] | State And Municipal Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	141,085		142,873
Level 2 [Member] | Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	104,819		77,321
Level 2 [Member] | Other Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	36		36
Level 2 [Member] | Money Market Investments Related To The Deferred Compensation Plan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets at fair value	0		0
Level 2 [Member] | Forward Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets at fair value	2,175	[2]	6,584	[2]
Level 2 [Member] | Liabilities Related To The Deferred Compensation Plan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total liabilities at fair value	0		0
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [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, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	0		0
Level 3 [Member] | Obligations Of Government-Sponsored Enterprises [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	0	[1]	0	[1]
Level 3 [Member] | State And Municipal Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	0		0
Level 3 [Member] | Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	2,588		2,588
Level 3 [Member] | Other Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments subtotal	0		0
Level 3 [Member] | Money Market Investments Related To The Deferred Compensation Plan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets at fair value	0		0
Level 3 [Member] | Forward Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets at fair value	0	[2]	0	[2]
Level 3 [Member] | Liabilities Related To The Deferred Compensation Plan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [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.