Share Based Award Stock compensation and related tax benefits (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation	$ 12,827	$ 9,592	$ 5,434
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	4,922	3,567	2,052
Indirect tax benefit from stock options	1,997	$ 209	$ 866
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 22,700
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	1 year
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	2,763,300
Time-based stock option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, Grants in Period, Gross	22,816	492,935	244,440
Time based options grant date fair value	$ 590	$ 7,311	$ 3,934
Terms of Award	5 years 7 months	4 years 8 months	4 years 7 months
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate	25.90%	26.70%	29.20%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate	1.70%	1.40%	0.80%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate	0.00%	0.00%	0.00%
Options, Grants in Period, Weighted Average Exercise Price	$ 93.30	$ 58.92	$ 62.12
Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 25.86	$ 14.83	$ 16.09
Performance stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, Grants in Period, Gross	244,825	699,625
Performance stock options total grant date fair value	$ 6,087	$ 13,344
Terms of Award	3 years	4 years
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate	30.86%	31.70%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate	2.30%	2.90%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate	0.00%	0.00%
Options, Grants in Period, Weighted Average Exercise Price	$ 91.88	$ 58.90
Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 24.86	$ 19.07

Indirect tax benefit from the stock compensation cost received upon the exercise of stock options

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Performance stock options total grant date fair value

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Time based options grant date fair value

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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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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.

+ References

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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-Subparagraph (f)(2)(iii)
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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

+ References

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-Publisher FASB
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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

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-Publisher FASB
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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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-Publisher FASB
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- Definition

Gross number of share options (or share units) granted during the period.

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No definition available.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Subparagraph (d)(1)
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- Definition

Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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