Earnings per Share - Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	12 Months Ended
Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share, Basic and Diluted [Abstract]
Net income	$ 15,510	$ 17,662	$ 16,468	$ 16,079	$ 18,372	$ 14,964	$ 4,357	$ 12,850	$ 65,719	$ 50,543	$ 44,094
Net income allocated to unvested restricted stock awards									(236)	(333)	(409)
Net income allocated to common shares									$ 65,483	$ 50,210	$ 43,685
Weighted average shares outstanding									29,300	29,370	26,862
Average unvested restricted stock awards									(107)	(193)	(256)
Denominator for basic earnings per share—weighted-average shares outstanding	29,232	29,211	29,181	29,146	29,161	29,232	29,176	29,140	29,193	29,177	26,606
Effect of dilutive securities—employee stock options and restricted stock units									68	82	102
Denominator for diluted earnings per share—adjusted weighted-average shares outstanding	29,313	29,285	29,243	29,205	29,220	29,318	29,271	29,234	29,261	29,259	26,708
Basic earnings per share	$ 0.53	$ 0.60	$ 0.56	$ 0.55	$ 0.63	$ 0.51	$ 0.15	$ 0.44	$ 2.24	$ 1.72	$ 1.64
Diluted earnings per share	$ 0.53	$ 0.60	$ 0.56	$ 0.55	$ 0.63	$ 0.51	$ 0.15	$ 0.44	$ 2.24	$ 1.72	$ 1.64
Average anti-dilutive options and restricted stock units excluded from computation of diluted earnings per share									325	319	169

Amount of increase (decrease) to net income used for calculating diluted earnings per share (EPS), resulting from the assumed exercise of stock options or restrictive stock units (RSUs).

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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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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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent, and includes adjustments resulting from the assumption that dilutive convertible securities were converted, options or warrants were exercised, or that other shares were issued upon the satisfaction of certain conditions.

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