Fair Value Measurement (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Financial assets:
Available-for-sale investments (substantially restricted)	$ 85,281	$ 102,771
Fair Value, Measurements, Recurring [Member]
Financial assets:
Investment related to deferred compensation trust	8,327	8,118
Total financial assets	95,031	111,288
Fair Value, Measurements, Recurring [Member] \| Forward Contracts [Member]
Financial liabilities:
Forward contracts	214	46
United States government agencies [Member]
Financial assets:
Available-for-sale investments (substantially restricted)	8,970	8,827
United States government agencies [Member] \| Fair Value, Measurements, Recurring [Member]
Financial assets:
Available-for-sale investments (substantially restricted)	8,970	8,827
Residential mortgage-backed securities - agencies [Member]
Financial assets:
Available-for-sale investments (substantially restricted)	49,614	69,712
Residential mortgage-backed securities - agencies [Member] \| Fair Value, Measurements, Recurring [Member]
Financial assets:
Available-for-sale investments (substantially restricted)	49,614	69,712
Other asset-backed securities [Member]
Financial assets:
Available-for-sale investments (substantially restricted)	26,697	24,232
Other asset-backed securities [Member] \| Fair Value, Measurements, Recurring [Member]
Financial assets:
Available-for-sale investments (substantially restricted)	26,697	24,232
Forward Contracts [Member] \| Fair Value, Measurements, Recurring [Member]
Financial assets:
Forward contracts	1,423	399
Level 1 [Member] \| Fair Value, Measurements, Recurring [Member]
Financial assets:
Investment related to deferred compensation trust	8,327	8,118
Total financial assets	8,327	8,118
Level 2 [Member] \| Fair Value, Measurements, Recurring [Member]
Financial assets:
Total financial assets	60,007	78,938
Level 2 [Member] \| Fair Value, Measurements, Recurring [Member] \| Forward Contracts [Member]
Financial liabilities:
Forward contracts	214	46
Level 2 [Member] \| United States government agencies [Member] \| Fair Value, Measurements, Recurring [Member]
Financial assets:
Available-for-sale investments (substantially restricted)	8,970	8,827
Level 2 [Member] \| Residential mortgage-backed securities - agencies [Member] \| Fair Value, Measurements, Recurring [Member]
Financial assets:
Available-for-sale investments (substantially restricted)	49,614	69,712
Level 2 [Member] \| Forward Contracts [Member] \| Fair Value, Measurements, Recurring [Member]
Financial assets:
Forward contracts	1,423	399
Level 3 [Member] \| Fair Value, Measurements, Recurring [Member]
Financial assets:
Total financial assets	26,697	24,232
Level 3 [Member] \| Other asset-backed securities [Member]
Financial assets:
Available-for-sale investments (substantially restricted)	26,697	24,232
Level 3 [Member] \| Other asset-backed securities [Member] \| Fair Value, Measurements, Recurring [Member]
Financial assets:
Available-for-sale investments (substantially restricted)	$ 26,697	$ 24,232

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 represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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Fair values as of the balance sheet date of all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

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- Definition

Derivative instrument obligations meeting the definition of a liability which the Company is a party to as of the balance sheet date.

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