Earnings per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands			3 Months Ended								12 Months Ended
	Apr. 27, 2016	Jan. 26, 2016	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net income attributable to Stewart			$ 11,373	$ 17,554	$ 22,377	$ (3,781)	$ 15,060	$ 10,944	$ 18,568	$ 4,087	$ 47,523	$ 48,659	$ 55,478
Less: Cash paid on Class B Common Shares conversion											0	0	(12,000)
Adjusted net income for calculating basic and diluted EPS											$ 47,523	$ 48,659	$ 43,478
Denominator (000):
Basic average shares outstanding											23,543	23,445	23,364
Average number of dilutive shares relating to restricted shares and units											142	152	108
Diluted average shares outstanding											23,685	23,597	23,472
Basic earnings per share attributable to Stewart (USD per share)											$ 2.02	$ 2.08	$ 1.86
Diluted earnings per share attributable to Stewart (USD per share)			$ 0.48	$ 0.74	$ 0.95	$ (0.16)	$ 0.64	$ 0.46	$ 0.79	$ 0.17	$ 2.01	$ 2.06	$ 1.85
Conversion, Class B Common Stock to Common Stock
Numerator:
Less: Cash paid on Class B Common Shares conversion	$ (12,000)	$ (12,000)									$ (12,000)		$ (12,000)