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Share-Based Compensation (Details) (USD $) | 9 Months Ended | 0 Months Ended | 9 Months Ended | 0 Months Ended
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Sep. 30, 2013 | Sep. 30, 2012 | Mar. 01, 2013 Performance share units | Sep. 30, 2013 Performance share units Percentile_Rank | Sep. 30, 2013 Restricted shares | Sep. 30, 2013 Options | Mar. 01, 2013 2013 PSU Grants Performance share units
Potential earned PSUs payout for defined levels of performance under awards |  |  |  |  |  |  |
Earned PSUs payout (as a percent of PSUs granted) on 75th or greater percentile rank |  |  |  | 200.00% |  |  |
Earned PSUs payout (as a percent of PSUs granted) on 50th percentile rank |  |  |  | 100.00% |  |  |
Earned PSUs payout (as a percent of PSUs granted) on 25th percentile rank |  |  |  | 50.00% |  |  |
Performance share units granted on percentile rank below 25th (as a percent) |  |  |  | 0.00% |  |  |
The number of percentile ranks to fall between to earn interpolated PSUs between such percentile ranks, conditioned on the percentile rank exceeding 25% |  |  |  | 2 |  |  |
Performance period of the award (in years) |  |  |  | 3 years |  |  |
Assumptions used to value stock awards |  |  |  |  |  |  |
Baseline value per common share (in dollars per share) |  |  |  | $ 25.85 |  |  |
Expected volatility of common shares (as a percent) |  |  |  | 29.50% |  |  |
Risk-free interest rate (as a percent) |  |  |  | 0.33% |  |  |
Shares |  |  |  |  |  |  |
Stock awards granted (in shares or units) |  |  |  |  | 177,510 |  | 69,579
Weighted Average Grant Date Fair Value |  |  |  |  |  |  |
Aggregate grant date fair value |  |  | $ 1,900,000 |  | $ 4,700,000 |  |
Weighted average grant date fair value (in dollars per share) |  |  |  | $ 26.84 | $ 26.24 |  |
Exercised (in shares) | 32,756 | 44,624 |  |  |  | 32,756 |
Weighted average exercise price (in dollars per share) |  |  |  |  |  | $ 19.45 |
Aggregate intrinsic value of options exercised (in dollars) |  |  |  |  |  | 237,000 |
Other Share-based Compensation Additional Disclosures |  |  |  |  |  |  |
Shares vested (in shares) |  |  |  |  | 222,381 |  |
Weighted average fair value of shares vested (in dollars per share) |  |  |  |  | $ 31.54 |  |
Aggregate intrinsic value of restricted common shares, forfeiture restrictions lapsed |  |  |  |  | $ 5,900,000 |  |

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- Definition The number of percentile ranks to fall between to earn interpolated PSUs between such percentile ranks, conditioned on the percentile rank exceeding 25%. + References No definition available. + Details
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- Definition The aggregate fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References No definition available. + Details
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- Definition The total intrinsic value of equity-based payment equity instruments, excluding stock (or unit) options, that vested during the reporting period as calculated by applying the disclosed pricing methodology. + References No definition available. + Details
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- Definition Represents the baseline common share value that is used in valuing the grant date fair value of awards. + References No definition available. + Details
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- Definition Represents the earned performance share units payout, as a percentage of performance share units granted, if the entity's total shareholder return relative to a peer group of companies ranks at the 25th percentile. + References No definition available. + Details
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- Definition Represents the earned performance share units payout, as a percentage of performance share units granted, if the entity's total shareholder return relative to a peer group of companies ranks at the 50th percentile. + References No definition available. + Details
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- Definition Represents the earned performance share units payout, as a percentage of performance share units granted, if the entity's total shareholder return relative to a peer group of companies ranks at the 75th percentile or greater. + References No definition available. + Details
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- Definition Represents the earned performance share units payout percentage based on percentile rank below 25. + References No definition available. + Details
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- Definition Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, 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 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target 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)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target 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)(2)(iii)(1) -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 The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement. + 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 The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over 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 (f)(2)(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The risk-free interest rate assumption that is used in valuing an option on its own 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 (f)(2)(iv) -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 Weighted average price at which option holders acquired shares when converting their stock options into shares. + References No definition available. + Details
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- Definition Number of share options (or share units) exercised during the current period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.28,29) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 5: 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)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 + Details
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