Organization and Significant Accounting Policies - Initial public offering (Details) - Subsequent Event - USD ($) $ / shares in Units, $ in Millions	Nov. 28, 2018	Oct. 24, 2018
IPO
Initial public offering
Cumulative common stock sold		16,000,000
Company's common stock sold		2,500,000
Common stock sold by selling stockholders		13,500,000
Public offering, shares issued price (per share)		$ 18.00
Net proceeds after deducting underwriting discounts and commissions		$ 42.4
IPO underwriting discounts and commissions		2.6
IPO offering costs incurred		$ 4.4
Additional allotment option
Initial public offering
Common stock sold by selling stockholders	918,830	2,400,000
Option to purchase additional shares from selling stockholders, period		30 days
Public offering, shares issued price (per share)	$ 18.00