Earnings per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net income attributable to Stewart	$ (31)	$ 66,108	$ 19,306	$ (6,768)	$ 11,373	$ 17,554	$ 22,377	$ (3,781)	$ 78,615	$ 47,523	$ 48,659
Denominator (000):
Basic average shares outstanding (in shares)									23,611	23,543	23,445
Average number of dilutive shares relating to restricted shares and units (in shares)									142	142	152
Diluted average shares outstanding (in shares)									23,753	23,685	23,597
Basic earnings per share attributable to Stewart (in usd per share)									$ 3.33	$ 2.02	$ 2.08
Diluted earnings per share attributable to Stewart (in usd per share)	$ 0	$ 2.78	$ 0.81	$ (0.29)	$ 0.48	$ 0.74	$ 0.95	$ (0.16)	$ 3.31	$ 2.01	$ 2.06