Stockholders' Equity- Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended	12 Months Ended
	Jun. 30, 2018	May 31, 2018	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class Of Stock [Line Items]
Proceeds from offering, net of underwriting discounts and commissions and offering expenses				$ 181,863	$ 133,862	$ 61,148
Preferred stock, shares authorized				5,000,000	5,000,000
Preferred stock, par value				$ 0.0001	$ 0.0001
Preferred stock, shares issued				0	0
Preferred stock, shares outstanding				0	0
Follow-On-Offering
Class Of Stock [Line Items]
Common stock shares issued		3,750,000
Common stock shares issued, price per share		$ 49.00
Proceeds from offering, net of underwriting discounts and commissions and offering expenses			$ 181,900
Over Allotment Option
Class Of Stock [Line Items]
Common stock shares issued	211,147
Common stock shares issued, price per share	$ 49.00		$ 49.00
Proceeds from offering, net of underwriting discounts and commissions and offering expenses			$ 9,700