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As of the balance sheet date, the projected compensation cost in remaining period of current year for equity-based awards made to employees under equity-based compensation awards that have yet to vest.

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No definition available.

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As of the balance sheet date, the projected compensation cost in fifth fiscal year of equity-based awards made to employees under equity-based compensation awards that have yet to vest.

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As of the balance sheet date, the projected compensation cost in fourth fiscal year of equity-based awards made to employees under equity-based compensation awards that have yet to vest.

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As of the balance sheet date, the projected compensation cost in sixth fiscal year of equity-based awards made to employees under equity-based compensation awards that have yet to vest.

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As of the balance sheet date, the projected compensation cost in third fiscal year of equity-based awards made to employees under equity-based compensation awards that have yet to vest.

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No definition available.

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As of the balance sheet date, the projected compensation cost in second fiscal year of equity-based awards made to employees under equity-based compensation awards that have yet to vest.

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No definition available.

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Number of stock award and incentive plan approved by shareholders to provide incentive to key individuals.

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Number of votes per share entitled to class of shares.

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Aggregate number of common shares reserved for future issuance.

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Unrecognized cost of unvested options awarded to employees as compensation.

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Amount of cash outflow for realized tax benefit related to deductible compensation cost reported on the entity's tax return for equity instruments in excess of the compensation cost for those instruments recognized for financial reporting purposes.

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The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

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Additional share-based compensation cost recognized as a result of an occurrence of an event that accelerates its recognition.

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No definition available.

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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 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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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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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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Number of shares for which recognition of compensation cost was accelerated.

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Percentage of vesting of share-based compensation awards.

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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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Stockholders' Equity, Voting Rights, Stock Award and Incentive Plan (Details) $ / shares in Units, $ in Thousands					3 Months Ended							9 Months Ended		12 Months Ended
	Sep. 17, 2018 $ / shares shares	Aug. 07, 2018 $ / shares shares	Apr. 04, 2018 $ / shares shares	Jan. 05, 2018 shares	Sep. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) $ / shares shares	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2018 USD ($) VoteperShare Plan $ / shares shares	Sep. 30, 2017 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares
Stock Award and Incentive Plan [Abstract]
Number of incentive plans \| Plan												1
Compensation record expenses due to accelerated vesting												$ 200
Actual and projected stock based compensation expense for RSA shares and options [Abstract]
Actual stock based compensation expense					$ 496	$ 351	$ 187	$ 1,488	$ 2,103	$ 4,381	$ 699	1,042	$ 7,181	$ 8,671
2018					1,606							1,606
2019					2,288							2,288
2020					2,288							2,288
2021					1,685							1,685
2022					1,316							1,316
2023					500							500
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Compensation cost related to non-vested options not yet recognized					$ 8,600							$ 8,600
Stock Options [Member] \| Maximum [Member]
Stock Award and Incentive Plan [Abstract]
Term of nonqualified stock options												10 years
Restricted Stock Awards [Member]
Stock Award and Incentive Plan [Abstract]
RSAs granted (in shares) \| shares	5,000	162,450	270,500
Grant date fair value (in dollars per share) \| $ / shares	$ 25.74	$ 25.16	$ 24.77
RSA shares outstanding (in shares) \| shares					434,750			19,400	164,050			434,750	164,050	19,400
Average weighted grant price (in dollars per share) \| $ / shares					$ 24.93			$ 65.67	$ 66.84			$ 24.93	$ 66.84	$ 65.67
Number of shares with accelerated vesting (in shares) \| shares				19,400
Restricted Stock Awards [Member] \| ASU 2016-09 [Member]
Stock Award and Incentive Plan [Abstract]
Tax benefit from stock based compensation expenses												$ 100
Restricted Stock Awards [Member] \| Vesting in Three Years from Date of Grant [Member]
Stock Award and Incentive Plan [Abstract]
Award vesting percentage												30.00%
Award vesting period												3 years
Restricted Stock Awards [Member] \| Vesting in Five Years from Date of Grant [Member]
Stock Award and Incentive Plan [Abstract]
Award vesting percentage												70.00%
Award vesting period												5 years
Restricted Stock Awards [Member] \| Vesting in Year Four from Date of Grant [Member]
Stock Award and Incentive Plan [Abstract]
Award vesting percentage												10.00%
Restricted Stock Awards [Member] \| Vesting in Year Five from Date of Grant [Member]
Stock Award and Incentive Plan [Abstract]
Award vesting percentage												10.00%
Restricted Stock Awards [Member] \| Vesting in Year Six from Date of Grant [Member]
Stock Award and Incentive Plan [Abstract]
Award vesting percentage												10.00%
Restricted Stock Awards [Member] \| Vesting in Year Seven from Date of Grant [Member]
Stock Award and Incentive Plan [Abstract]
Award vesting percentage												10.00%
Restricted Stock Awards [Member] \| Vesting in Year Eight from Date of Grant [Member]
Stock Award and Incentive Plan [Abstract]
Award vesting percentage												10.00%
Restricted Stock Awards [Member] \| Vesting in Year Nine from Date of Grant [Member]
Stock Award and Incentive Plan [Abstract]
Award vesting percentage												10.00%
Restricted Stock Awards [Member] \| Vesting in Year Ten from Date of Grant [Member]
Stock Award and Incentive Plan [Abstract]
Award vesting percentage												10.00%
Q1 [Member]
Actual and projected stock based compensation expense for RSA shares and options [Abstract]
2019					$ 572							$ 572
2020					572							572
2021					572							572
2022					329							329
2023					329							329
Q2 [Member]
Actual and projected stock based compensation expense for RSA shares and options [Abstract]
2019					572							572
2020					572							572
2021					423							423
2022					329							329
2023					128							128
Q3 [Member]
Actual and projected stock based compensation expense for RSA shares and options [Abstract]
2019					572							572
2020					572							572
2021					361							361
2022					329							329
2023					43							43
Q4 [Member]
Actual and projected stock based compensation expense for RSA shares and options [Abstract]
2018					572							572
2019					572							572
2020					572							572
2021					329							329
2022					329							329
2023					$ 0							$ 0
Class A [Member]
Voting Rights [Abstract]
Number of votes per share \| VoteperShare												1
Class A [Member] \| Maximum [Member]
Stock Award and Incentive Plan [Abstract]
Number of shares reserved for issuance under each plan (in shares) \| shares					7,500,000							7,500,000
Class B [Member]
Voting Rights [Abstract]
Number of votes per share \| VoteperShare												10