Represents the number of separate employee groups eligible for share-based compensation.

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- Definition

Represents the period of historical option activity considered to determine expected option life.

+ References

No definition available.

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- Definition

Represents the maximum allowable contribution by eligible employees as a percentage of base earnings.

+ References

No definition available.

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- Definition

Share based compensation arrangement by share based payment award maximum employee contribution in calendar year.

+ References

No definition available.

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- Definition

Represents the common stock purchase price as a percentage of fair market value.

+ References

No definition available.

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- Definition

The period of time, from the grant date until the time at which the share-based [option] award expires.

+ References

No definition available.

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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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-Paragraph 2
-Subparagraph (i)
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- Definition

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.

+ References

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- Definition

Amount of cash outflow to satisfy an employee's income tax withholding obligation as part of a net-share settlement of a share-based award.

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- Definition

Amount of cash inflow from issuance of shares under share-based compensation arrangement. Issuance includes, but is not limited to, exercise of stock options and similar instruments.

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- Definition

Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

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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- Definition

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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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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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- Definition

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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- Definition

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

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Stock-Based Compensation - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) item shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 shares	Dec. 31, 2014 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation cost	$ 7,200,000
Cash received from stock option exercises and employee stock purchases	16,200,000
Cash used for shares withheld to satisfy employee tax obligations for RSUs and PRSUs converted	$ 5,700,000
Shares authorized for future grant under stock plan (in shares) \| shares	1,600,000
Non-qualified stock options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period	3 years
Options expiration period	10 years
Period of historical option activity considered to determine expected option life	10 years
Number of separate employee groups \| item	2
Unrecognized compensation cost	$ 1,200,000	$ 1,100,000
Non-qualified stock options \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Period over which unrecognized compensation costs will be recognized	1 year
Non-qualified stock options \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Period over which unrecognized compensation costs will be recognized	3 years
RSUs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares outstanding \| shares	490,739	500,000	500,000	500,000
RSUs \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Period over which unrecognized compensation costs will be recognized	1 year
RSUs \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Period over which unrecognized compensation costs will be recognized	3 years
PRSUs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares outstanding \| shares	367,760	400,000	400,000	400,000
Unrecognized compensation cost	$ 2,000,000
Performance period	3 years	3 years	3 years
PRSUs \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Period over which unrecognized compensation costs will be recognized	1 year
Performance period	3 years
PRSUs \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Period over which unrecognized compensation costs will be recognized	3 years
Employee stock purchase plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum contribution by eligible employees as percentage of base earnings (as a percent)	10.00%
Maximum contribution by eligible employees in a calendar year	$ 25,000
Common stock purchase price as percentage of fair market value (as a percent)	85.00%
Shares purchased under employee stock purchase plan (in shares) \| shares	52,824	47,952