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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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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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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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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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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- Definition

Number of additional shares authorized for issuance under an established share-based compensation plan.

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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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- Definition

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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- Definition

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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- Definition

Number of non-vested options outstanding.

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Accounting for Stock Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	May 19, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2013	Dec. 31, 2014	May 16, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option grant expiration period					10 years
Number of performance based unvested stock options, restricted stock outstanding		282,100	210,481	179,026		177,084
Unrecognized compensation cost related to nonvested options and restricted options		$ 18,593	$ 17,258
Unrecognized share-based compensation cost recognition period		3 years
Share based compensation expense		$ 12,727	$ 8,147	$ 12,316
Weighted average grant date fair value of options granted		$ 9.11	$ 10.74	$ 10.60
Total intrinsic value of options exercised		$ 4,715	$ 2,456	$ 18,745
Total fair value of restricted shares vested		$ 6,006	3,865	4,088
Stock Appreciation Rights (SARs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of performance based unvested stock options, SARs outstanding		0
Total intrinsic value of options exercised		$ 1,495	$ 261	$ 4,185
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of performance based unvested stock options, restricted stock outstanding		0
Employee and Consultants \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share based compensation, requisite service period		3 years
Employee and Consultants \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share based compensation, requisite service period		5 years
Director
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share based compensation, requisite service period		1 year
2013 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for grant		1,751,554
Number of shares authorized for grant							3,500,000
Number of increased shares available for grant	2,000,000
Equity Incentive Plan Twenty Eleven and Two Thousand and Six
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for grant							0