Employee Incentive Plans, Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common shares authorized for issuance under Equity Incentive Plan	2,722,222
Number of common shares available for additional awards under Equity Incentive Plan	709,362
Non-cash compensation expense	$ 9.3	$ 6.8	$ 6.6
Recognized tax benefit relating to non-cash compensation expense	3.5	2.5	2.4
Total grant-date fair value for shares granted	11.8	14.8
Total grant-date fair value for shares that vested	$ 5.8	$ 5.5	5.1
Fully-vested options outstanding	16,645	16,645
Exercise price of options to purchase common stock	$ 80.01	$ 80.01
Remaining contractual life of options outstanding	1 year 3 months	2 years 3 months
Grant date fair value of options outstanding	$ 39.90
Stock options granted	0	0
Stock options exercised	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested Options Forfeited, Number of Shares	0
Stock options expired	0	0
Issuance of common shares to non-employee directors	$ 0.2	$ 0.2	$ 0.2
Shares Paid for Tax Withholding for Share Based Compensation	37,009	33,696	40,075
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	1 year
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years
Restricted stock units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common share received by the employee on vesting of restricted stock unit	1
Restricted Stock And Restricted Stock Units Member
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-cash compensation expense	$ 4.4	$ 3.9	$ 4.3
Unrecognized gross compensation costs (in millions of dollars)	$ 5.8
Expected period (in years) over which the remaining gross compensation costs will be recognized	1 year 11 months 10 days
EVA-Based Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years
Non-cash compensation expense	$ 0.9	1.0	2.3
Unrecognized gross compensation costs (in millions of dollars)	$ 0.3
Expected period (in years) over which the remaining gross compensation costs will be recognized	2 months 14 days
EVA-Based Performance Shares \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	0.00%
EVA-Based Performance Shares \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	200.00%
TSR-Based Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-cash compensation expense	$ 4.0	$ 1.9	$ 0.0
Unrecognized gross compensation costs (in millions of dollars)	$ 7.5
Expected period (in years) over which the remaining gross compensation costs will be recognized	1 year 11 months 10 days
TSR-Based Performance Shares \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	0.00%
TSR-Based Performance Shares \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	200.00%

Number of common share received by the employee on vesting of restricted stock unit.

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- Definition

Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Granted In Period Total Fair Value

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No definition available.

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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.

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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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- Definition

Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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- Definition

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

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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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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- Definition

As of the balance sheet date, the number of shares into which fully vested and expected to vest stock options outstanding can be converted under the option plan.

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Percentage of vesting of share-based compensation awards.

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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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- Definition

Number of non-vested options forfeited.

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- Definition

For net-share settlement of share-based awards when the employer settles employees' income tax withholding obligations, this element represents the number of shares the employees use to repay the employer.

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

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Value of stock issued in lieu of cash for services contributed to the entity. Value of the stock issued includes, but is not limited to, services contributed by vendors and founders.

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