Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	1,595,675
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	1,072,750
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Compensation cost not yet recognized, period for recognition	1 year 2 months 12 days
Profit Sharing and 401(k) Plan (the “401(k) Plan”), Shares in 401(k) Plan	1,454,844
Employee Stock Purchase Plan, Maximum Payroll Deduction	15.00%
Employee Stock Purchase Plan, Percent of Total Share Value	95.00%
Proceeds from ESPP	$ 0.8
Shares from ESPP	16,413	16,717	22,567
Stock Repurchase Program, Authorized Amount	$ 200.0
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding, ending balance (in shares)	0
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	$ 15.8	$ 13.4	$ 8.8
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding, beginning balance (in shares)	681	451	565
Outstanding, beginning balance, Weighted Average Grant Date Fair Value per Share (in dollars per share)	$ 39.15	$ 32.73	$ 31.38
Granted (in shares)	259	572	228
Granted, Weighted Average Grant Date Fair Value per Share (in dollars per share)	$ 51.31	$ 43.17	$ 33.40
Vested (in shares)	(372)	(307)	(300)
Vested, Weighted Average Grant Date Fair Value Per Share (in dollars per share)	$ 43.89	$ 36.24	$ 31.50
Forfeited (in shares)	(44)	(35)	(42)
Forfeited, Weighted Average Grant Date Fair Value per Share (in dollars per share)	$ 43.51	$ 40.97	$ 33.38
Outstanding, ending balance (in shares)	524	681	451
Outstanding, ending balance, Weighted Average Grant Date Fair Value per Share (in dollars per share)	$ 41.51	$ 39.15	$ 32.73
Allocated Share-based Compensation Expense, Net of Tax	$ 11.4	$ 9.2	$ 5.8
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	10.0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Total Grant Date Fair Value	$ 16.7	$ 11.5	$ 10.3
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding, ending balance (in shares)	0

Employee Stock Purchase Plan, Maximum Payroll Deduction Percent

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Employee Stock Purchase Plan, Percent of Total Share Value

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No definition available.

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- Definition

Equity-based compensation cost, net of tax, during the period with respect to the award, which will be recognized in income (as well as the total recognized tax benefit) or capitalized as part of the cost of an asset.

+ References

No definition available.

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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Total Grant Date Fair Value

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No definition available.

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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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- Definition

Sum of the allocated, committed-to-be-released and suspense shares of the entity held by the plan.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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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).

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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).

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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.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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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.

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- Definition

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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No definition available.

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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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Number of shares issued during the period as a result of an employee stock purchase plan.

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Aggregate change in value for stock issued during the period as a result of employee stock purchase plan.

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Amount of stock repurchase plan authorized.

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No definition available.

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