Business Segment Information (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Reconciliation of segment profit to income before income taxes
Segment profit	$ 59,248	$ 69,431	$ 203,529	$ 189,646
Stock compensation expense	(4,524)	(4,468)	(14,764)	(13,935)
Depreciation and amortization	(17,654)	(15,239)	(50,770)	(45,172)
Interest expense	(789)	(537)	(2,191)	(1,713)
Interest income	291	350	1,002	1,619
Income before income taxes	$ 36,572	$ 49,537	$ 136,806	$ 130,445

The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

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Aggregate revenue less cost of goods and services sold or operating expenses directly attributable to the revenue generation activity.

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Sum of operating profit and nonoperating income or expense before Income or Loss from equity method investments, income taxes, extraordinary items, and noncontrolling interest.

+ References

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- Definition

The cost of borrowed funds accounted for as interest that was charged against earnings during the period.

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Income derived from investments in debt securities and on cash and cash equivalents the earnings of which reflect the time value of money or transactions in which the payments are for the use or forbearance of money.

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The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

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