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Cash paid for expenses incurred during underwriting activities (the process to review insurance applications, evaluate risks, accept or reject applications, and determine the premiums to be charged) for insurance companies.

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Gross number of share options (or share units) granted during the period.

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Stockholders' Equity - Additional Information (Details) - USD ($)									9 Months Ended
	Sep. 18, 2019	Nov. 09, 2018	Aug. 03, 2018	May 14, 2018	Apr. 09, 2018	Jan. 29, 2018	Jan. 23, 2018	Sep. 19, 2017	Sep. 30, 2019	Dec. 31, 2018
Stockholders Equity [Line Items]
Stock issued during period, shares, new issues			2,555,555
Public offering price per share			$ 18.00
Proceeds from issuance initial public offering, after deduction underwriting discounts, commissions			$ 42,700,000
Payments for Underwriting Expense			$ 3,300,000
Number of share outstanding									1,385,664	781,725
Awards granted under the plan									1,063,150
Unrecognized compensation expense									$ 6,700,000
Share based compensation arrangement by share based payment award, Average remaining vesting period									2 years 6 months
Weighted average grant date fair value of options granted									$ 8.03
Warrants outstanding									0	0
Series J Warrants
Stockholders Equity [Line Items]
Warrants expired for aggregate share of common stock to purchase							2,942
Series K Warrants
Stockholders Equity [Line Items]
Warrants expired for aggregate share of common stock to purchase						2,262
Series M Warrants
Stockholders Equity [Line Items]
Warrants expired for aggregate share of common stock to purchase					301,452
2018 Stock Incentive Plan
Stockholders Equity [Line Items]
Number of common stock authorized for issuance				500,000					403,495
Share-based compensation arrangement by share-based payment award, description									In addition, the number of shares authorized for issuance under the 2018 Plan is automatically increased (the “evergreen provision”) on the first day of each fiscal year beginning on January 1, 2019, and ending on (and including) January 1, 2028, in an amount equal to the lesser of (i) 4% of the outstanding shares of common stock on the last day of the immediately preceding fiscal year, or (ii) another amount (including zero) determined by the Company’s Board of Directors. Any shares subject to awards granted under the 2018 Plan that are forfeited or terminated before being exercised or settled, or are not delivered to the participant because such award is settled in cash, will again become available for issuance under the 2018 Plan. Shares withheld to satisfy the grant, exercise price or tax withholding obligation related to an award will again become available for issuance under the 2018 Plan.
Share-based compensation arrangement by share-based payment award, expiration date									Jan. 01, 2028
Share-based compensation arrangement by share-based payment award, percentage of outstanding our common stock									4.00%
Options contractual term				10 years
Available for the grant of future awards									89,815
2018 Stock Incentive Plan \| Executive Officers and Employees
Stockholders Equity [Line Items]
Share-based compensation arrangement by share-based payment award, stock options vesting period				4 years
2018 Stock Incentive Plan \| Executive Officers and Employees \| One-year Anniversary of the Grant Date
Stockholders Equity [Line Items]
Share-based compensation arrangement by share-based payment award, Vesting percentage Share-based compensation arrangement by share-based payment award, Vesting percentage				25.00%
2018 Stock Incentive Plan \| Executive Officers and Employees \| Quarterly over Remaining Three Years
Stockholders Equity [Line Items]
Share-based compensation arrangement by share-based payment award, Vesting percentage Share-based compensation arrangement by share-based payment award, Vesting percentage				75.00%
2018 Stock Incentive Plan \| Executive Officers and Employees \| January 1, 2021
Stockholders Equity [Line Items]
Share-based compensation arrangement by share-based payment award, Vesting percentage Share-based compensation arrangement by share-based payment award, Vesting percentage	50.00%
2018 Stock Incentive Plan \| Executive Officers and Employees \| January 1, 2022
Stockholders Equity [Line Items]
Share-based compensation arrangement by share-based payment award, Vesting percentage Share-based compensation arrangement by share-based payment award, Vesting percentage	50.00%
2013 Stock Incentive Plan
Stockholders Equity [Line Items]
Number of common stock authorized for issuance								165,000
Options contractual term								10 years
Awards granted under the plan									0
2010 Stock Incentive Plan
Stockholders Equity [Line Items]
Number of common stock authorized for issuance								470,170
Options contractual term								10 years
Awards granted under the plan									0
Maximum \| 2010 and 2013 Stock Incentive Plan
Stockholders Equity [Line Items]
Number of share outstanding				635,170
Over-Allotment Option
Stockholders Equity [Line Items]
Stock issued during period, shares, new issues			333,333
At-the-Market Facility \| Maximum
Stockholders Equity [Line Items]
Aggregate offering price of common stock		$ 50,000,000