Stock-Based Compensation Plans Stock Performance Rights (Details) - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Stock Performance Rights
Accrued Employee Benefits, Current	$ 13,458,000	$ 8,712,000
Valuation assumptions:
Allocated Share-based Compensation Expense	100,000	200,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Share-based Liabilities Paid	$ 100,000	300,000
Stock Performance Rights
Stock Performance Rights
Weighted average estimated value of SPRs outstanding (per share)	$ 14.96
Valuation assumptions:
Expected volatility, minimum, percent	36.70%
Expected volatility, maximum, percent	42.70%
Risk-free rate of return, minimum	2.50%
Risk-free rate of return, maximum	2.60%
Expected annual dividend	$ 0.00
Allocated Share-based Compensation Expense	$ 4,800,000	$ 1,200,000
Number of SPRs
Outstanding on December 31, 2017	961,554
Granted	44,737
Exercised	(13,270)
Cancelled	(34,500)
Outstanding on December 31, 2018	958,521	961,554
Exercisable on December 31, 2018	848,503
Weighted Average Exercise Price
Outstanding on December 31, 2017	$ 19.75	$ 19.76
Granted		24.70
Exercised		22.16
Cancelled		25.52
Outstanding on December 31, 2018		19.75
Exercisable on December 31, 2018		$ 19.11
SPRs outstanding, intrinsic value	$ 11,500,000
Total unrecognized compensation cost	$ 800,000
Unrecognized cost, period for recognition	1 year 7 months 6 days
Exercised	193,835
Vested in period, fair value	$ 2,000,000
Weighted average remaining contractual term, SPRs outstanding	3 years 7 months 6 days
Weighted average remaining contractual term, SPRs exercisable	3 years 3 months 18 days
Stock Performance Rights \| Minimum
Stock Performance Rights
Life of award	7 years
Award vesting period		1 year
Valuation assumptions:
Expected term	1 year
Stock Performance Rights \| Maximum
Stock Performance Rights
Life of award	10 years
Award vesting period	3 years
Valuation assumptions:
Expected term	4 years 6 months

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Carrying value as of the balance sheet date of obligations, excluding pension and other postretirement benefits, incurred through that date and payable for perquisites provided to employees pertaining to services received from them. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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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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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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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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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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Per share weighted average intrinsic value of equity-based compensation awards not vested. Excludes stock and unit options.

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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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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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Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of cash paid related to share-based compensation liabilities.

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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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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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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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The estimated amount of dividends to be paid to holders of the underlying shares (expected dividends) over the option's term. Dividends are taken into account because payment of dividends to shareholders reduces the fair value of the underlying shares, and option holders generally do not receive dividends.

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The estimated measure of the maximum 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.

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The maximum risk-free interest rate assumption that is used in valuing an option on its own shares.

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The minimum risk-free interest rate assumption that is used in valuing an option on its own shares.

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Number of non-option equity instruments exercised by participants.

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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.

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Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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