Accounting for Stock-based Compensation - Schedule of Stock-based Compensation Expense (Details) - USD ($) $ 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]
Stock-Based Compensation Recognized	$ 19,581	$ 17,544	$ 15,943
Stock-Based Compensation Unrecognized	$ 27,361
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-Based Compensation Recognized		164	909
Stock-Based Compensation Unrecognized Weighted- Average Period to Recognize (Year)	0 years
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-Based Compensation Recognized	$ 7,410	7,080	6,325
Stock-Based Compensation Unrecognized	$ 13,484
Stock-Based Compensation Unrecognized Weighted- Average Period to Recognize (Year)	1 year 9 months 18 days
Cash Settled RSUs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-Based Compensation Recognized	$ 8,214	7,253	7,091
Stock-Based Compensation Unrecognized	$ 10,550
Stock-Based Compensation Unrecognized Weighted- Average Period to Recognize (Year)	1 year 7 months 6 days
Non-Employee Director Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-Based Compensation Recognized	$ 764	671	741
Stock-Based Compensation Unrecognized	$ 327
Stock-Based Compensation Unrecognized Weighted- Average Period to Recognize (Year)	4 months 24 days
Performance Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-Based Compensation Recognized	$ 3,193	$ 2,376	$ 877
Stock-Based Compensation Unrecognized	$ 3,000
Stock-Based Compensation Unrecognized Weighted- Average Period to Recognize (Year)	1 year 6 months

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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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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