Introduction (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
	May 06, 2019	Mar. 30, 2019	Mar. 31, 2018
Subsidiary, Sale of Stock [Line Items]
Sale of stock, issuance costs		$ 946	$ 0
Subsequent event
Subsidiary, Sale of Stock [Line Items]
Underwriting discounts and commissions	$ 19,400
Subsequent event | IPO
Subsidiary, Sale of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	11,068,750
Sale of stock, price per share (in dollars per share)	$ 25.00
Proceeds from IPO, net	$ 252,500
Sale of stock, issuance costs	$ 4,800
Number of common stock shares converted	41,562,111
Number of shares issued for each share of convertible preferred stock converted (in shares)	1
Subsequent event | Over-allotment option
Subsidiary, Sale of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	1,443,750
Common Stock | Subsequent event | IPO
Subsidiary, Sale of Stock [Line Items]
Number of shares able to purchase	160,767