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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Amount of tax benefit from exercise of stock options granted under share-based compensation arrangement.

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Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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

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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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Percentage of vesting of share-based compensation awards.

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

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Stock Options (Narrative) (Details) - USD ($)	12 Months Ended
Stock Options (Narrative) (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	May 07, 2015	May 07, 2009
Qualified Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value of options granted (in dollars per share)	$ 36.00	$ 27.48	$ 27.63
Allocated Share-based Compensation Expense	$ 597,000	$ 787,000	$ 735,000
Total unrecognized compensation cost related to non-vested share-based compensation arrangements	$ 998,000
Granted (in shares)	10,750	21,000	29,500
Period cost is expected to be recognized (years)	5 years
Exercise of stock options (in shares)	54,945	43,775	75,355
Non Qualified Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	$ 22,000	$ 27,000	$ 35,000
Total unrecognized compensation cost related to non-vested share-based compensation arrangements	$ 30,000
Granted (in shares)	0	0	0
Period cost is expected to be recognized (years)	5 years
Exercise of stock options (in shares)	45,400	14,900	4,800
Proceeds from stock options exercised	$ 1,032,000	$ 205,000	$ 55,000
Tax deductions from option exercises	0	657,000	187,000
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	1,250,000	$ 600,000	$ 287,000
Total unrecognized compensation cost related to non-vested share-based compensation arrangements	$ 3,544,000
Period cost is expected to be recognized (years)	4 years
Weighted average remaining contractual life (years)	2 years 8 months 8 days	2 years 10 months 20 days	3 years 1 month 10 days
Restricted Stock Units (RSUs) \| Year One after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	25.00%
Award vesting period (years)	1 year
Restricted Stock Units (RSUs) \| Year Two after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	25.00%
Restricted Stock Units (RSUs) \| Year Three after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	25.00%
Restricted Stock Units (RSUs) \| Year Four after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	25.00%
2015 ISO Plan \| Qualified Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for options to be issued (in shares)				400,000
2015 ISO Plan \| Qualified Stock Options \| Year One after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (years)	1 year
2015 ISO Plan \| Qualified Stock Options \| Year One after Grant Date \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	20.00%
2015 ISO Plan \| Qualified Stock Options \| Year Two after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	20.00%
2015 ISO Plan \| Qualified Stock Options \| Year Three after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	20.00%
2015 ISO Plan \| Qualified Stock Options \| Year Four after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	20.00%
2015 ISO Plan \| Qualified Stock Options \| Year Five after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	20.00%
2009 Equity Incentive Plan \| Non Qualified Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for options to be issued (in shares)					400,000
2009 Equity Incentive Plan \| Non Qualified Options \| Year One after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (years)	1 year
2009 Equity Incentive Plan \| Non Qualified Options \| Year One after Grant Date \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	20.00%
2009 Equity Incentive Plan \| Non Qualified Options \| Year Two after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	20.00%
2009 Equity Incentive Plan \| Non Qualified Options \| Year Three after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	20.00%
2009 Equity Incentive Plan \| Non Qualified Options \| Year Four after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	20.00%
2009 Equity Incentive Plan \| Non Qualified Options \| Year Five after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	20.00%