Earnings Per Share - Computation of Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income per consolidated statements of income	$ 10,504	$ 10,486	$ 8,656	$ 9,529	$ 9,541	$ 8,556	$ 29,646	$ 27,626
Net income allocated to participating securities	(27)			(49)			(103)	(140)
Net income allocated to common stock	10,477			9,480			29,543	27,486
Distributed earnings allocated to common stock	3,837			3,478			10,664	9,432
Undistributed earnings allocated to common stock	$ 6,640			$ 6,002			$ 18,879	$ 18,054
Weighted average common shares outstanding, including shares considered participating securities	48,085			49,909			48,563	49,892
Less: Average participating securities	(124)			(226)			(168)	(252)
Weighted average shares	47,961			49,683			48,395	49,640
Basic earnings per common share	$ 0.22			$ 0.19			$ 0.61	$ 0.55
Weighted average common shares outstanding for basic earnings per common share	47,961			49,683			48,395	49,640
Add: Dilutive effects of assumed exercises of stock options and LTIP awards	203			264			201	262
Weighted average shares and dilutive potential common shares	48,164			49,947			48,596	49,902
Diluted earnings per common share	$ 0.22			$ 0.19			$ 0.61	$ 0.55

Average participating securities.

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Net income or loss available to common stockholders, basic, less allocation to participating securities.

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Undistributed earnings allocated to common shareholders.

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The total amount of dividends declared in the period for each class of stock and the contractual amount of dividends (or interest on participating income bonds) that must be paid for the period (for example, unpaid cumulative dividends). Dividends declared in the current period do not include dividends declared in respect of prior-period unpaid cumulative dividends. Preferred dividends that are cumulative only if earned are deducted only to the extent that they are earned.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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