Fair Value Measurements (Assets and Liabilities Measured at Fair Value on Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Assets
Cash equivalents	$ 82,762	$ 28,364
Marketable securities
Investment at fair value	269,151	287,081
Total assets at fair value	351,913	315,445
Liabilities
Deferred compensation plan liabilities	6,641	6,055
Total liabilities at fair value	6,641	6,055
Equity Securities [Member]
Marketable securities
Investment at fair value	11,206	9,174
Municipal Securities [Member]
Marketable securities
Investment at fair value	251,304	271,852
Mutual Funds [Member]
Marketable securities
Investment at fair value	6,641	6,055
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Cash equivalents	0	0
Marketable securities
Investment at fair value	17,847	15,229
Total assets at fair value	17,847	15,229
Liabilities
Deferred compensation plan liabilities	6,641	6,055
Total liabilities at fair value	6,641	6,055
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Equity Securities [Member]
Marketable securities
Investment at fair value	11,206	9,174
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Municipal Securities [Member]
Marketable securities
Investment at fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Mutual Funds [Member]
Marketable securities
Investment at fair value	6,641	6,055
Significant Other Observable Inputs (Level 2) [Member]
Assets
Cash equivalents	82,762	28,364
Marketable securities
Investment at fair value	251,304	271,852
Total assets at fair value	334,066	300,216
Liabilities
Deferred compensation plan liabilities	0	0
Total liabilities at fair value	0	0
Significant Other Observable Inputs (Level 2) [Member] \| Equity Securities [Member]
Marketable securities
Investment at fair value	0	0
Significant Other Observable Inputs (Level 2) [Member] \| Municipal Securities [Member]
Marketable securities
Investment at fair value	251,304	271,852
Significant Other Observable Inputs (Level 2) [Member] \| Mutual Funds [Member]
Marketable securities
Investment at fair value	0	0
Significant Unobservable Inputs (Level 3) [Member]
Assets
Cash equivalents	0	0
Marketable securities
Investment at fair value	0	0
Total assets at fair value	0	0
Liabilities
Deferred compensation plan liabilities	0	0
Total liabilities at fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] \| Equity Securities [Member]
Marketable securities
Investment at fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] \| Municipal Securities [Member]
Marketable securities
Investment at fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] \| Mutual Funds [Member]
Marketable securities
Investment at fair value	$ 0	$ 0

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.

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