Earnings per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net income attributable to Stewart	$ 88,663	$ 55,909	$ 237,718	$ 95,232
Denominator (000):
Basic average shares outstanding (in shares)	26,873	25,148	26,803	24,151
Average number of dilutive shares relating to options (in shares)	190	0	160	0
Average number of dilutive shares relating to grants of restricted units and shares (in shares)	175	149	127	105
Diluted average shares outstanding (in shares)	27,238	25,297	27,090	24,256
Basic earnings per share attributable to Stewart (in usd per share)	$ 3.30	$ 2.22	$ 8.87	$ 3.94
Diluted earnings per share attributable to Stewart (in usd per share)	$ 3.26	$ 2.21	$ 8.78	$ 3.93