Description of Business - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		6 Months Ended		12 Months Ended
	Jul. 02, 2018	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Description Of Business [Line Items]
Common stock, par value per share		$ 0.01		$ 0.01
Common stock, shares authorized for issuance		413,918,000		413,918,000
Preferred stock, shares authorized for issuance		0		0
Preferred stock, par value per share		$ 0.01		$ 0.01
Cash and cash equivalents		$ 14,544	$ 26,233	$ 29,147	$ 17,040
Accumulated deficit		209,939		196,946
Cash flows from operating activities		13,397	$ 9,481	$ 11,100
$35.0 Million Credit Facility | Oxford Finance LLC
Description Of Business [Line Items]
Borrowings outstanding under credit facility		$ 30,000
Credit facility maturity date		Mar. 01, 2022
Subsequent Event
Description Of Business [Line Items]
IPO closing date	Jul. 02, 2018
Initial Public Offering | Subsequent Event
Description Of Business [Line Items]
Net proceeds from initial public offering	$ 100,000
Underwriting discounts and commissions before deducting offering expense	$ 7,500
Common stock, par value per share	$ 0.01
Common stock, shares authorized for issuance	200,000,000
Preferred stock, shares authorized for issuance	10,000,000
Preferred stock, par value per share	$ 0.01
Initial Public Offering | Subsequent Event | Common Stock
Description Of Business [Line Items]
Common stock shares issued and sold	6,325,000
Exercise of underwriter's option to purchase additional shares	825,000
Issuance price per share	$ 17.00
Convertible preferred stock converted into common stock	11,000,000