Stock-Based Compensation - Additional Information (Detail) - USD ($)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted (in shares)	0
Options outstanding (in shares)	102,216	135,250
Excess tax benefits from stock based compensation, operating activities	$ 587,000	$ 0	$ 0
Excess tax benefits of stock based compensation, financing activities	0	43,000	59,000
Share-based compensation expense	2,325,000	1,899,000	1,605,000
Aggregate intrinsic value of options exercised	337,000	292,000
Exercise of stock options	321,000	285,000	124,000
Fair value of options vested	$ 35,000	$ 35,000
2009 Equity Compensation Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, common stock, shares authorized (in shares)	2,300,000
Expiration period of stock option plan	10 years
Expiration period of after termination of service of plan	90 days
Expiration period of after death or disability of the grantee	1 year
2000 Equity Compensation Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, common stock, shares authorized (in shares)	2,613,185
Expiration period of stock option plan	10 years
Expiration period of after termination of service of plan	30 days
Expiration period of after death or disability of the grantee	1 year
Stock options granted (in shares)	0
Somerset Hills' Stock Option Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding (in shares)	20,774	23,415
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 14,000	$ 35,000	35,000
Stock Options \| 2009 Equity Compensation Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost	0
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost	6,000
Share-based compensation expense	287,000	$ 353,000	$ 497,000
Fair value of options vested	$ 322,000
Granted (usd per share)	$ 18.20
Unrecognized compensation expense, period of recognition	1 month 2 days
Granted (in shares)	13,176
Restricted Stock \| 2009 Equity Compensation Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted (in shares)	13,176	23,952	0
Granted (usd per share)	$ 18.20	$ 10.02
Vesting period	1 year	1 year
Allocated share based compensation expense	$ 240,000	$ 240,000
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (usd per share)	$ 19.92
Granted (in shares)	132,523
RSUs \| 2009 Equity Compensation Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost	$ 1,800,000
Granted (usd per share)	$ 19.92	$ 10.45	$ 11.08
Vesting period	3 years	3 years	3 years
Allocated share based compensation expense	$ 2,000,000	$ 1,500,000	$ 1,100,000
Share-based compensation expense	$ 880,000	$ 630,000	$ 506,000
Unrecognized compensation expense, period of recognition	1 year 1 month 6 days
Granted (in shares)	132,523	180,926	137,009
RSUs \| 2009 Equity Compensation Program \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	2 years	2 years
RSUs \| 2009 Equity Compensation Program \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years	3 years
Director
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding (in shares)	81,442	111,829,000

Average annual compensation cost over vesting period.

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Share based compensation arrangement by share based payment award expiration period after death of grantee.

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Share based compensation arrangement by share based payment award expiration period after termination of service.

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share based compensation arrangement by share based payment award options grants in period weighted average remaining contractual term maximum.

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

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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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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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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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Net number of non-option equity instruments granted to participants.

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

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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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