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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net income (loss) attributable to Stewart			$ 15,060	$ 10,944	$ 18,568	$ 4,087	$ 16,699	$ 26,375	$ 23,599	$ (11,195)	$ 48,659	$ 55,478	$ (6,204)
Less: Cash paid on Class B Common Shares conversion											0	(12,000)	0
Adjusted net income (loss) for calculating basic and diluted EPS											$ 48,659	$ 43,478	$ (6,204)
Denominator (000):
Basic average shares outstanding											23,445	23,364	23,544
Average number of dilutive shares relating to restricted shares grants											152	108	0
Diluted average shares outstanding											23,597	23,472	23,544
Basic earnings (loss) per share attributable to Stewart (USD per share)											$ 2.08	$ 1.86	$ (0.26)
Diluted earnings (loss) per share attributable to Stewart (USD per share)			$ 0.64	$ 0.46	$ 0.79	$ 0.17	$ 0.71	$ 1.12	$ 0.49	$ (0.48)	$ 2.06	$ 1.85	$ (0.26)
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)