Represents the number of separate incentive compensation programs within a incentive compensation plan.

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Period which an employee's right to exercise an award.

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Represents the number of share based compensation plans utilized by the entity.

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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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Amount of tax benefit 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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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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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 number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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

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Number of options outstanding, including both vested and non-vested options.

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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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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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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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Weighted average remaining contractual term for option awards outstanding, 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 options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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Purchase price of common stock expressed as a percentage of its fair value.

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

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SHARE-BASED AWARDS - SUMMARY (Details) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) plan $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($)
Share-based expense (net of estimated forfeitures)
Total share-based expense	$ 12,100	$ 11,100	$ 9,800
Intrinsic value of options exercised	500	700	2,000
Tax benefit realized upon option exercise	2,700	6,800	5,900
Fair value of stock vested	10,800	$ 17,300	$ 15,800
Stock options
Share-based expense (net of estimated forfeitures)
Unrecognized compensation cost	$ 0
Weighted average exercise price
Outstanding, weighted average exercise price, beginning of period (in dollars per share) \| $ / shares	$ 21.54
Exercised, weighted average exercise price (in dollars per share) \| $ / shares	20.18
Outstanding, weighted average exercise price, end of period (in dollars per share) \| $ / shares	21.81	$ 21.54
Exercisable, weighted average exercise price, end of period (in dollars per share) \| $ / shares	$ 21.81
Outstanding, weighted average contractual life, end of period	2 years 7 months 6 days
Exercisable, weighted average contractual life, end of period	2 years 7 months 6 days
Outstanding, aggregate intrinsic value, end of period (in dollars)	$ 1,998
Exercisable, aggregate intrinsic value, end of period (in dollars)	1,998
Non-vested restricted stock units and performance-based equity awards
Share-based expense (net of estimated forfeitures)
Unrecognized compensation cost	$ 11,600
Unrecognized compensation cost, weighted average period for recognition	1 year 8 months 12 days
Restricted Stock Units
Share-based compensation
Options granted, weighted average grant-date fair value (in dollars per share) \| $ / shares	$ 31.15
2016 Plan
Share-based compensation
Common stock initially available for future issuance (in shares) \| shares	2,500
Number of separate incentive compensation programs \| plan	4
Number of share based compensation plans within the entity's incentive compensation programs \| plan	3
2007 Plan \| Discretionary Grant Program
Share-based compensation
Minimum exercise price as a percentage of fair market value of common stock	100.00%
Exercisable period	3 years
Expiration Term	10 years
2007 Plan \| Stock options
Activity in the entity's stock option plans
Outstanding, beginning of period (in shares) \| shares	235
Exercised (in shares) \| shares	(39)
Outstanding, end of period (in shares) \| shares	196	235
Exercisable, end of period (in shares) \| shares	196
2007 Plan \| Time-Based Restricted Stock Units \| Stock Issuance Program
Share-based compensation
Vesting period of awards granted	3 years
2007 Plan \| Performance-Based Restricted Stock Units \| Stock Issuance Program
Share-based compensation
Vesting period of awards granted	3 years