Stock-based Compensation and Employee Benefits - Narrative (Details) - USD ($)	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 500,000
Stock options [Member] \| NBH Holdings Corp. 2014 Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award Vesting Rights, Percentage	33.30%
Contractual term (in years)	10 years
Stock based compensation expense	$ 47,000	$ 173,000
Unrecognized compensation expense	$ 500,000
Unrecognized compensation cost, weighted-average period, years	1 year 10 months 24 days
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (in shares)	3,749
Weighted average grant-date fair value, Granted (in dollars per share)	$ 35.75
Restricted Stock [Member] \| NBH Holdings Corp. 2014 Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense	$ 200,000	400,000
Unrecognized compensation expense	$ 1,500,000
Unrecognized compensation cost, weighted-average period, years	2 years
Performance stock units \| NBH Holdings Corp. 2014 Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense	$ 200,000	$ 200,000
Unrecognized compensation expense	$ 1,800,000
Unrecognized compensation cost, weighted-average period, years	1 year 8 months 12 days
Performance stock units \| NBH Holdings Corp. 2014 Omnibus Incentive Plan [Member] \| EPS target
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of awards based on performance type	60.00%
Performance stock units \| NBH Holdings Corp. 2014 Omnibus Incentive Plan [Member] \| TSR target
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of awards based on performance type	40.00%
Employee Stock [Member] \| Employee Stock Purchase Plan 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized	400,000
Maximum stock purchases by employees, value	$ 25,000
Maximum stock purchases by employees (in shares)	2,000
Discount on purchase of common stock (as a percent)	90.00%
Offering period for employee stock purchases	6 months
Employees purchased shares (in shares)	6,201	5,960
Shares available for issuance	336,443
Minimum \| Stock options [Member] \| NBH Holdings Corp. 2014 Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	1 year
Minimum \| Restricted Stock [Member] \| NBH Holdings Corp. 2014 Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	1 year
Minimum \| Performance stock units \| NBH Holdings Corp. 2014 Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of initial target awards	0
Maximum \| Stock options [Member] \| NBH Holdings Corp. 2014 Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Maximum \| Restricted Stock [Member] \| NBH Holdings Corp. 2014 Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Maximum \| Performance stock units \| NBH Holdings Corp. 2014 Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of initial target awards	150

Percentage of award based on specified performance condition.

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Percentage of initial target of share-based compensation awards.

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The maximum value of shares, which an employee can purchase per calendar year.

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Share Based Compensation Arrangement By Share Based Payment Award Options Granted Contractual Term

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Discount rate from fair value on purchase date that participants pay for shares.

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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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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, 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 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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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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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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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Percentage of vesting of share-based compensation awards.

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

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Number of shares issued during the period as a result of an employee stock purchase plan.

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