Stock-Based Compensation - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost related to stock grants and vesting of restricted stock units	$ 1,638	$ 1,958
Dividends declared not paid on restricted stock units	84	0
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of restricted stock units vested and released	4,533	3,614
Compensation cost related to stock grants and vesting of restricted stock units	1,638	1,958
One-time expense for modification of vesting terms	249
Restricted Stock Units (RSUs) \| Director
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost related to stock grants and vesting of restricted stock units	172	177
Stock-Settled EBI Units and Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to nonvested stock-settled EBI units and restricted stock units	$ 12,004	$ 15,696
Expected weighted-average period to be recognized	2 years 4 months 2 days	2 years 9 months 11 days
Dividends declared not paid on restricted stock units	$ 293
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase price percentage of subsequent offering periods			95.00%
Maximum number of shares issuable (in shares)			200,000
Maximum number of shares per participant (in shares)			725
Maximum worth of award per participant			$ 25,000
Shares issued under plan (in shares)	10,613	16,537
Number of shares reserved for issuance (in shares)	2,421,743	2,444,428

Share based compensation arrangement by share based payment award maximum purchase of common stock value per employee.

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Aggregate number of common shares reserved for future issuance.

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- Definition

Carrying value as of the balance sheet date of dividends declared but unpaid on equity securities issued by the entity and outstanding.

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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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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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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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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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- Definition

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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- Definition

The highest quantity of shares an employee can purchase under the plan per period.

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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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- Definition

An excess of the fair value of the modified award over the fair value of the award immediately before the modification.

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- Definition

Number of share instruments newly issued under a share-based compensation plan.

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- Definition

Purchase price of common stock expressed as a percentage of its fair value.

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