Fair Value of Financial Instruments (Details) (USD $)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Impairment Charges	$ 123,573,000
Goodwill, Impairment Loss	99,501,000	21,310,000	0
Goodwill	1,291,231,000	1,237,607,000	1,092,480,000
Carrying value and fair value of long-term debt
Variable-rate long-term debt, Carrying Value	592,422,000	573,984,000
Variable-rate long-term debt, Fair Value	592,422,000	573,984,000
Vetstreet [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Impairment Charges	22,900,000
Goodwill, Impairment Loss	99,500,000
Goodwill	8,800,000
Long-Lived Assets	$ 28,700,000

The charge against earnings resulting from the aggregate write down of all assets from their carrying value to their fair value.

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Carrying amount as of the balance sheet date, which is the cumulative amount paid and (if applicable) the fair value of any noncontrolling interest in the acquiree, adjusted for any amortization recognized prior to the adoption of any changes in generally accepted accounting principles (as applicable) and for any impairment charges, in excess of the fair value of net assets acquired in one or more business combination transactions.

+ References

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+ Details

- Definition

Loss recognized during the period that results from the write-down of goodwill after comparing the implied fair value of reporting unit goodwill with the carrying amount of that goodwill. Goodwill is assessed at least annually for impairment.

+ References

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+ Details

- Definition

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 notes payable as of the balance sheet date.

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