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Stock-Based Compensation Plans (Summary of Stock Option Activity) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands | 12 Months Ended
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Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Employee Stock Option Plan |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] |  |  |
Shares, Outstanding at Beginning of Year | 17,829 | 18,000 | 17,722
Shares, Granted | 2,966 | 5,757 | 5,462
Shares, Exercised | (2,344) | (5,224) | (4,450)
Shares, Forfeited | (759) | (704) | (734)
Shares, Outstanding at End of Year | 17,692 | 17,829 | 18,000
Shares, Exercisable at End of Year | 6,858 | 4,564 | 5,490
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) | $ 13 | $ 12 | $ 11
Wtd. Avg. Ex. Price, Granted (usd per share) | 17 | 15 | 13
Wtd. Avg. Ex. Price, Exercised (usd per share) | 12 | 11 | 8
Wtd. Avg. Ex. Price, Forfeited (usd per share) | 14 | 13 | 12
Wtd. Avg. Ex. Price, Outstanding at End of Year (usd per share) | 14 | 13 | 12
Wtd. Avg. Ex. Price, Exercisable at End of Year (usd per share) | $ 13 | $ 12 | $ 12
Option expiration period, years | 3 years | 3 years 6 months | 3 years 4 months 24 days
Wtd. Avg. Remaining Contract Life, Exercisable at End of Year | 2 years 1 month 6 days | 2 years 3 months 18 days | 2 years 3 months 18 days
Aggregate Intrinsic Value, Exercised | $ 11,596 | $ 26,618 | $ 20,884
Aggregate Intrinsic Value, Outstanding at End of Year | 45,842 | 90,759 | 85,633
Aggregate Intrinsic Value, Exercisable at End of Year | $ 23,917 | $ 28,342 | $ 28,302
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 | 381 | 462 | 468
Shares, Granted | 49 | 98 | 84
Shares, Exercised | (57) | (167) | (90)
Shares, Forfeited | 0 | (12) | 0
Shares, Outstanding at End of Year | 373 | 381 | 462
Shares, Exercisable at End of Year | 373 | 381 | 462
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) | 17 | 14 | 12
Wtd. Avg. Ex. Price, Exercised (usd per share) | 11 | 10 | 10
Wtd. Avg. Ex. Price, Forfeited (usd per share) | 0 | 16 | 0
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) | $ 13 | $ 12 | $ 11
Option expiration period, years | 6 years 4 months 24 days | 6 years 8 months 12 days | 6 years 4 months 24 days
Wtd. Avg. Remaining Contract Life, Exercisable at End of Year | 6 years 4 months 24 days | 6 years 8 months 12 days | 6 years 4 months 24 days
Aggregate Intrinsic Value, Exercised |  | $ 893 | $ 300
Aggregate Intrinsic Value, Outstanding at End of Year | $ 1,069 | 2,137 | 2,491
Aggregate Intrinsic Value, Exercisable at End of Year | $ 1,069 | $ 2,137 | $ 2,491

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- Definition 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. + 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 (c)(1)(iii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition 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. + 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 (c)(1)(iii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition 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. + 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 (d)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition 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. + 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 (c)(1)(iv)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Net number of share options (or share units) granted during the period. + 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 (c)(1)(iv)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Number of options outstanding, including both vested and non-vested options. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan. + 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 (c)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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