Employee Benefit Plans and Stock-based Compensation - RSU (Details) - USD ($)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Weighted Average Grant Date Fair Value [Roll Forward]
Common stock reserved for future issuance	4,535
Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock options exercised (in shares)	762,000	555,000	119,000
Intrinsic value of options exercised	$ 4,030,000	$ 1,302,000	$ 118,000
Weighted Average Grant Date Fair Value [Roll Forward]
Weighted-average grant date fair value of stock options granted (in dollars per share)	$ 3.67	$ 1.85	$ 0.88
Common stock reserved for future issuance	2,666
Restricted Stock Awards
Shares [Roll Forward]
Non-vested, beginning of period (in shares)	325	546	261
Granted (in shares)	312	136	547
Vested (in shares)	(157)	(150)	(215)
Forfeited (in shares)		(207)	(47)
Non-vested, end of period (in shares)	480	325	546
Weighted Average Grant Date Fair Value [Roll Forward]
Non-vested, beginning of period (in dollars per share)	$ 3.27	$ 2.39	$ 2.71
Granted (in dollars per share)	9.15	4.66	2.42
Vested (in dollars per share)	3.13	2.34	2.81
Forfeited (in dollars per share)		2.55	2.47
Non-vested, end of period (in dollars per share)	$ 7.13	$ 3.27	$ 2.39
Total fair value of restricted stock awards vested	$ 490,000	$ 351,000	$ 605,000
Unrecognized compensation expense related to restricted stock awards	$ 3,100,000
Weighted average remaining contractual terms	2 years
Common stock reserved for future issuance	480
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	$ 1,700,000
Value of estimated forfeitures	$ 190,000
Weighted-average period of amortization	2 years 3 months 18 days
Weighted Average Grant Date Fair Value [Roll Forward]
Common stock reserved for future issuance	1,389

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

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Aggregate number of common shares reserved for future issuance.

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

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