Employee Stock Plans - Stock Option Activity Table (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares outstanding	1,860,693	2,228,108
Shares outstanding, weighted-average exercise price	$ 40.67	$ 35.92
Shares granted	355,869
Shares granted, weighted-average exercise price	$ 57.02
Shares exercised	(655,706)
Shares exercised, weighted-average exercise price	$ 33.23
Shares forfeited	(67,578)
Shares forfeited, weighted-average exercise price	$ 42.58
Shares exercisable	905,258
Shares exercisable, weighted-average exercise price	$ 34.37
Shares outstanding, weighted-average remaining contractual life	76 months
Shares exercisable, weighted-average remaining contractual life	54 months
Shares outstanding, aggregate intrinsic value	$ 32,128
Shares exercisable, aggregate intrinsic value	$ 21,289

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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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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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-Name Accounting Standards Codification

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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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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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Gross 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 remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

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