Stock-Based Compensation - Stock Options Activity Rollforward (Details) - $ / shares	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	0	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding options, beginning of year, number of shares	1,387,378
Exercised, number of shares	(441,241)
Forfeited, number of shares	(5,294)
Outstanding options, end of year, number of shares	940,843	1,387,378
Outstanding options exercisable, end of year, number of shares	940,843
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding options, beginning of year, weighted average exercise price	$ 17.06
Exercised, weighted average exercise price	17.68
Forfeited, weighted average exercise price	17.33
Outstanding options, end of year, weighted average exercise price	16.77	$ 17.06
Outstanding options exercisable, end of year, weighted average exercise price	$ 16.77
Outstanding options, end of year weighted average remaining contractual term	2 years 10 months 18 days
Outstanding options exercisable, end of year, weighted average remaining contractual term	2 years 10 months 18 days

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

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

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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

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