Stock-Based Compensation Plans (Summary of Stock Option Activity) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares, Outstanding at Beginning of Year	18,000	17,722	15,110
Shares, Granted	5,757	5,462	5,282
Shares, Exercised	(5,224)	(4,450)	(1,378)
Shares, Forfeited	(704)	(734)	(1,292)
Shares, Outstanding at End of Year	17,829	18,000	17,722
Shares, Exercisable at End of Year	4,564	5,490	6,006
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Wtd. Avg. Ex. Price, Outstanding at Beginning of Year (usd per share)	$ 12	$ 11	$ 11
Wtd. Avg. Ex. Price, Granted (usd per share)	$ 15	$ 13	$ 10
Wtd. Avg. Ex. Price, Exercised (usd per share)	$ 11	$ 8	$ 8
Wtd. Avg. Ex. Price, Forfeited (usd per share)	$ 13	$ 12	$ 11
Wtd. Avg. Ex. Price, Outstanding at End of Year (usd per share)	$ 13	$ 12	$ 11
Wtd. Avg. Ex. Price, Exercisable at End of Year (usd per share)	$ 12	$ 12	$ 10
Wtd. Avg. Remaining Contract Life, Outstanding at End of Year	3 years 6 months	3 years 4 months 24 days	3 years 4 months 24 days
Wtd. Avg. Remaining Contract Life, Exercisable at End of Year	2 years 3 months 18 days	2 years 3 months 18 days	2 years 2 months 12 days
Aggregate Intrinsic Value, Exercised	$ 26,618	$ 20,884	$ 3,810
Aggregate Intrinsic Value, Outstanding at End of Year	90,759	85,633	11,730
Aggregate Intrinsic Value, Exercisable at End of Year	28,342	28,302	7,617
Non-Employee Director Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares, Outstanding at Beginning of Year	462	468	384
Shares, Granted	98	84	84
Shares, Exercised	(167)	(90)	0
Shares, Forfeited	(12)	0	0
Shares, Outstanding at End of Year	381	462	468
Shares, Exercisable at End of Year	381	462	468
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Wtd. Avg. Ex. Price, Outstanding at Beginning of Year (usd per share)	$ 11	$ 11	$ 11
Wtd. Avg. Ex. Price, Granted (usd per share)	$ 14	$ 12	$ 11
Wtd. Avg. Ex. Price, Exercised (usd per share)	$ 10	$ 10	$ 0
Wtd. Avg. Ex. Price, Forfeited (usd per share)	$ 16	$ 0	$ 0
Wtd. Avg. Ex. Price, Outstanding at End of Year (usd per share)	$ 12	$ 11	$ 11
Wtd. Avg. Ex. Price, Exercisable at End of Year (usd per share)	$ 12	$ 11	$ 11
Wtd. Avg. Remaining Contract Life, Outstanding at End of Year	6 years 8 months 12 days	6 years 4 months 24 days	6 years 4 months 24 days
Wtd. Avg. Remaining Contract Life, Exercisable at End of Year	6 years 8 months 12 days	6 years 4 months 24 days	6 years 4 months 24 days
Aggregate Intrinsic Value, Exercised	893	300
Aggregate Intrinsic Value, Outstanding at End of Year	2,137	2,491	225
Aggregate Intrinsic Value, Exercisable at End of Year	$ 2,137	$ 2,491	$ 225

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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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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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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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 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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