Number of shares authorized for issuance to the Company's employee stock purchase plan

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Fair value of a share of common stock, percentage

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Percentage of ownership in subsidiaries

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Percentage of total combined voting power of the Company and our subsidiaries

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Number of stock units authorized for achievement of targeted performance

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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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Face amount or stated value per share of common stock.

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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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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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The amount of plan compensation cost recognized during the period.

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Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

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The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

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Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt.

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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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Discount rate from fair value on purchase date that participants pay for shares.

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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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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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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.

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

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Description of pertinent provisions of equity-based compensation awards that have actual or potential impact upon the company's financial statements.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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CAPITAL STOCK AND SHARE-BASED COMPENSATION - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 07, 2012	Jun. 06, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, authorized (shares)	60,000,000	60,000,000
Common stock, par value (usd per share)	$ 0.001	$ 0.001
Preferred stock, authorized (shares)	5,000,000	5,000,000
Preferred stock, par value (usd per share)	$ 0.001	$ 0.001
Common stock, issued (shares)	36,252,280	35,747,134
Common stock, outstanding (shares)	31,973,505	33,964,767
Preferred stock, issued (shares)	0	0
Percentage of ownership in subsidiaries	50.00%
Equity-based awards, number of shares authorized (shares)	2,500,000
Equity-based awards, shares available for grant (shares)	2,400,000
Percentage of total combined voting power of the Company and subsidiaries	10.00%
Percentage of market value for purchases under Employee Stock Purchase Program (percent)	85.00%
Common stock authorized for issuance under Employee Stock Purchase Plan (shares)	1,377,017
Employee Stock Purchase Plan expense	$ 0.5	$ 0.4	$ 0.4
Options granted (shares)	163,666
Tax benefit from stock option exercise	$ 1.6	0.3
Intrinsic value of options outstanding	66.9
Intrinsic value of options exerciseable	41.3
Intrinsic value of options exercised during the period	$ 9.7	$ 3.9
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term of share-based award	ten
Common stock authorized for issuance under Employee Stock Purchase Plan (shares)				4,500,000	2,500,000
Vesting period of equity-based awards	5 years
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of equity-based awards	12 months
Share-Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of share of common stock (percent)	100.00%
Share Based Awards to More Than Ten Percent Owner [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of share of common stock (percent)	110.00%
Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted (shares)	163,666	308,292	268,538
Stock compensation expense	$ 5.7	$ 5.6	$ 6.3
Unrecognized compensation expense	$ 5.1
Unrecognized compensation expense weighted-average period for recognitions (years)	1 year 8 months 12 days
Non-Vested Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense	$ 1.4	$ 1.7	$ 2.3
Unrecognized compensation expense	$ 0.5
Unrecognized compensation expense weighted-average period for recognitions (years)	4 months 24 days
Non-vested stock granted, weighted average grant date fair value (usd per share)	$ 80.54	$ 62.67	$ 50.55
Non-Vested Stock [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of equity-based awards	5 years
Non-Vested Stock [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of equity-based awards	1 year
Non-Vested Stock Units [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of equity-based awards	5 years
Non-Vested Stock Units [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of equity-based awards	1 year
Non-Vested Stock Units - Service-Based [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense	$ 4.5	$ 3.6	$ 3.6
Unrecognized compensation expense	$ 11.0
Unrecognized compensation expense weighted-average period for recognitions (years)	2 years 3 months 18 days
Non-vested stock granted, weighted average grant date fair value (usd per share)	$ 95.14	$ 53.79	$ 45.60
Non-Vested Stock Units - Service-Based and Performance-Based [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense	$ 5.8	$ 5.0	$ 3.7
Unrecognized compensation expense	$ 8.3
Unrecognized compensation expense weighted-average period for recognitions (years)	1 year 10 months 24 days
Non-vested stock granted, weighted average grant date fair value (usd per share)	$ 79.59	$ 52.99	$ 46.29
Performance-based award, target number of units to be received (shares)	115,338