Shareholders’ equity (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions			9 Months Ended
	May 07, 2018	May 02, 2018	Sep. 30, 2018
Shareholders’ equity
Offering price per share of shares issued	$ 28.50
Gross Proceeds From Issuance Initial Public Offering	$ 147,500
Proceeds from issuance initial public offering			$ 138,480
Expenses capitalized related to offering	$ 200
Shares authorized under offering program		5