Employee Benefit Plans and Stock-Based Compensation - RSU (Details) - USD ($) $ / shares in Units, shares in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Weighted Average Grant Date Fair Value [Roll Forward]
Common stock reserved for future issuance	4,940
Restricted Stock Awards
Shares [Roll Forward]
Non-vested, beginning of period (in shares)	633	480	325
Granted (in shares)	554	344	312
Vested (in shares)	(228)	(181)	(157)
Forfeited (in shares)	(20)	(10)
Non-vested, end of period (in shares)	939	633	480
Weighted Average Grant Date Fair Value [Roll Forward]
Non-vested, beginning of period (in dollars per share)	$ 6.85	$ 7.13	$ 3.27
Granted (in dollars per share)	3.60	6.02	9.15
Vested (in dollars per share)	6.46	6.04	3.13
Forfeited (in dollars per share)	7.16	6.65
Non-vested, end of period (in dollars per share)	$ 5.02	$ 6.85	$ 7.13
Total fair value of restricted stock awards vested	$ 1,500,000	$ 1,100,000	$ 490,000
Unrecognized compensation expense related to restricted stock awards	$ 4,200,000
Weighted average remaining contractual terms	1 year 7 months 6 days
Common stock reserved for future issuance	939
Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock options exercised (in shares)	113	238	762
Intrinsic value of options exercised	$ 266,000	$ 666,000	$ 4,030,000
Weighted Average Grant Date Fair Value [Roll Forward]
Common stock reserved for future issuance	2,953
2015 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation costs related to unvested stock options not yet recognized	$ 1,400,000
Value of estimated forfeitures	$ 110,000
Weighted-average period of amortization	2 years 10 months 24 days
Weighted Average Grant Date Fair Value [Roll Forward]
Common stock reserved for future issuance	1,048

Represents the value of estimated forfeiture of aggregate unrecognized cost of option awards.

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- Definition

Aggregate number of common shares reserved for future issuance.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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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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Unrecognized cost of unvested options awarded to employees as compensation.

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

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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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- 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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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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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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Number of share options (or share units) exercised during the current period.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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