Stock-Based Compensation Plans - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 6,585	$ 6,362
Stock-based compensation expense, tax benefits	1,200	$ 1,000
Total Shareholder Return (TSRs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs	$ 31,600
Unrecognized compensation costs, weighted-average recognition period	2 years 3 months 18 days
Restricted Share Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares vested	173,547
Shares withheld to pay employees' portion of minimum payroll withholding taxes	53,274
Unrecognized compensation costs	$ 26,700
Unrecognized compensation costs, weighted-average recognition period	1 year 10 months 24 days
LTIP Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs	$ 3,000
Unrecognized compensation costs, weighted-average recognition period	1 year
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incentive plan, weighted-average grant date fair value of stock options granted		$ 7.03
Incentive plan, total intrinsic value of stock options exercised	$ 5,300	$ 7,200
Unrecognized compensation costs	$ 1,100
Unrecognized compensation costs, weighted-average recognition period	10 months 24 days
Restricted Share Awards (RSAs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares vested	98,769
Shares withheld to pay employees' portion of minimum payroll withholding taxes	30,878
Unrecognized compensation costs	$ 1,900
Unrecognized compensation costs, weighted-average recognition period	10 months 24 days
Employee Stock Purchase Plan 2017 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued under ESPP	32,174	38,145

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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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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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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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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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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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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For net-share settlement of share-based awards when the employer settles employees' income tax withholding obligations, this element represents the number of shares the employees use to repay the employer.

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Number of shares issued during the period as a result of an employee stock purchase plan.

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