Share-Based Compensation - Additional Information (Detail)	12 Months Ended
Dec. 31, 2017 USD ($) $ / shares Plans shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of share-based compensation plans \| Plans	2
Intrinsic Value of Options, Exercised \| $	$ 0	$ 535,000	$ 902,000
Intrinsic Value of Options, Outstanding \| $	0		1,253,000
Intrinsic Value of Options, Exercisable \| $	$ 0		$ 1,253,000
Closing stock price per share \| $ / shares	$ 9.27	$ 20.90	$ 32.51
Proceeds from options exercised \| $	$ 0	$ 2,097,000	$ 1,939,000
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Payout based on economic profit performance against target economic profit goals	0.00%	0.00%	0.00%
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Payout based on economic profit performance against target economic profit goals	200.00%	200.00%	200.00%
Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation cost \| $	$ 0
Stock options granted \| shares	0	0
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock and restricted stock units granted \| shares	351,762	554,491	462,697
Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation cost \| $	$ 8,600,000
Restricted stock and restricted stock units granted \| shares	271,445	276,110	162,092
Vesting year	2020	2019	2018
Share-based compensation, weighed -average period for recognition	1 year 6 months
Non Employee Directors [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Compensation expense, directors fees \| $	$ 0	$ 100,000	$ 100,000
Accumulated number of stock units outstanding \| shares	36,379	40,189	41,051
Restricted stock and restricted stock units granted \| shares	150,361	55,120	30,778
Employees [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock and restricted stock units granted \| shares	57,641	383,196	333,268
Executive Officer [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock and restricted stock units granted \| shares	415,205	392,285	260,743
Terms of granting restricted stock and restricted stock units	the officer is still employed as of the anniversary date of the grant and the Company’s cumulative diluted adjusted earnings per share for the four calendar quarters immediately preceding the vesting date exceed the minimum as defined in the officers’ restricted stock agreement.
Executive Officer [Member] \| Restricted Stock [Member] \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period, in years	3 years

The number of share-based compensation plans outstanding during the period.

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Share based compensation arrangement by share based payment award, award vesting year.

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Share based compensation arrangement by share based payment payout percentage.

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Unrecognized cost of unvested share-based compensation awards.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
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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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Noninterest expense related to directors' fees which are fees paid by an Entity to its directors. Directors' fees may be paid in addition to salary and other benefits.

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Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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Per share amount received by subsidiary or equity investee for each share of common stock issued or sold in the stock transaction.

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

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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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Description of pertinent provisions of equity-based compensation awards that have actual or potential impact upon the company's financial statements.

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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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