Stock-Based Compensation - Schedule of Information Related to Outstanding SOSARS (Detail) - Stock Only Stock Appreciation Rights (SOSARs) [Member] - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Outstanding	2,736,616	2,199,742
Granted		743,925
Exercised	(33,050)	(53,190)
Canceled / forfeited	(17,630)	(108,945)
Ending Balance, Outstanding	2,685,936	2,781,532
Beginning Balance, Weighted Average Exercise Price, Outstanding	$ 17.64	$ 17.82
Weighted Average Exercise Price, Granted		17.54
Weighted Average Exercise Price, Exercised	14.65	9.91
Weighted Average Exercise Price, Canceled / forfeited	18.46	21.81
Ending Balance, Weighted Average Exercise Price, Outstanding	$ 17.67	17.74
Weighted average grant date fair value per share		$ 4.07
Aggregate grant date fair value		$ 3,013
Black-Scholes assumptions
Dividend yield		2.85%
Risk free rate of return		1.34%
Volatility		31.97%
Expected life		6 years

Share based compensation arrangement by share based payment award options grant date fair value.

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Share based compensation arrangement by share Based payment award options grant date fair value per share.

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

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Weighted average expected volatility rate of share-based compensation awards.

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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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For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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Weighted average price of options that were either forfeited or expired.

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- Definition

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

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- Definition

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

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

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

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- Definition

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

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- Definition

Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

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