Stock-Based Compensation - Summary of Activity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant date fair value of options granted (usd per share)	$ 2.89	$ 2.91	$ 2.66
Total intrinsic value of options exercised	$ 1,585	$ 300	$ 100
Stock-based compensation expense	5,100	7,100	5,100
Income tax expense	1,300	2,700	1,900
Nonvested stock awards (restricted stock and restricted stock units)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total vest date fair value of stock awards vested	$ 12,700	$ 300	$ 700

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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- Definition

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

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- Definition

Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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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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- Definition

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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