Equity Incentive Plan (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Options, Outstanding, Number, Beginning	1,008,476
Options, Grants in Period, Net of Forfeitures	43,943
Options, Exercises in Period	(163,120)
Options, Forfeitures in Period	(41,469)
Options, Outstanding, Number, Ending	847,830
Options, Exercisable, Number	676,202
Aggregate Intrinsic Value [Abstract]
Options, Outstanding, Intrinsic Value	$ 264.0	$ 392.2
Options, Exercisable, Intrinsic Value	$ 242.8
Weighted Average Exercise Price [Abstract]
Options, Outstanding, Weighted Average Exercise Price, Beginning	$ 232.99
Options, Grants in Period, Weighted Average Exercise Price	595.31
Options, Exercises in Period, Weighted Average Exercise Price	150.81
Options, Forfeitures in Period, Weighted Average Exercise Price	369.93
Options, Outstanding, Weighted Average Exercise Price, Ending	260.88
Options, Exercisable, Weighted Average Exercise Price	$ 208.01

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Weighted Average Exercise Price [Abstract]

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Number of share options (or share units) exercised during the current period.

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