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Employee Share-Based Incentive Compensation Plans (WTM Restricted Shares) (Details) (USD $) In Millions, except Share data, unless otherwise specified | 12 Months Ended |
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Dec. 31, 2011 | Dec. 31, 2013 Restricted Share Cliff Vesting in January 2016 [Member] | Dec. 31, 2012 Restricted Share Cliff Vesting in January 2015 [Member] | Dec. 31, 2012 Restricted Share Vesting Beginning in February 2014 [Member] Installment | Dec. 31, 2012 Restricted Share Cliff Vesting in July 2015 [Member] | Dec. 31, 2011 Restricted Share Cliff Vesting in January 2014 [Member] | Dec. 31, 2011 W T M Incentive Plan | Dec. 31, 2013 W T M Incentive Plan Restricted Stock | Dec. 31, 2012 W T M Incentive Plan Restricted Stock | Dec. 31, 2012 Restricted Share Vested in December 2012 [Member] Restricted Stock
Target Performance Share activity |  |  |  |  |  |  |  |  |  |  |  |  |
Beginning of period (in shares) |  |  |  |  |  |  | 46,250 |  | 69,910 |  | 72,000 |  |
Issued (in shares) |  | 25,720 | 27,960 | 3,000 | 1,200 | 27,250 | 27,250 |  | 25,720 |  | 32,160 |  |
Vested (in shares) |  |  |  |  |  |  | (1,500) | [1] | (1,500) | [1] | (32,945) | [1] |
Assumed forfeitures and cancellations (in shares) | 0 |  |  |  |  |  | 0 |  | 0 |  | (1,305) |  |
Ending of period (in shares) |  |  |  |  |  |  | 72,000 |  | 94,130 |  | 69,910 |  |
Unamortized grant date fair value |  |  |  |  |  |  |  |  |  |  |  |  |
Beginning balance |  |  |  |  |  |  | $ 14.1 |  | $ 16.8 |  | $ 13.3 |  |
Issued |  |  |  |  |  |  | 9.9 |  | 14.4 |  | 15.7 |  |
Assumed forfeitures and cancellations |  |  |  |  |  |  | 0 |  | 0 |  | (0.2) |  |
Expense recognized |  |  |  |  |  |  | (10.7) |  | (14.2) |  | (12.0) |  |
Ending balance |  |  |  |  |  |  | $ 13.3 |  | $ 17.0 |  | $ 16.8 |  |
Number of restricted shares installments |  |  |  | 2 |  |  |  |  |  |  |  |  | 5,000
[1] | During 2012, the Compensation Committee accelerated the vesting date for an installment of 5,000 restricted shares from January 20, 2013 to December 31, 2012.

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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 -Section F + Details
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- Definition Unrecognized cost of unvested share-based compensation awards. + 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 (i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting 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)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date. + 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)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting 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)(2)(iii)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Number of share instruments newly issued under a share-based compensation 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 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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