Schedule I - Financial Information of the Registrant (Parent Company) - Statements of Operations and Retained Earnings (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	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
Revenues
Investment income									$ 18,932	$ 18,925	$ 16,850
Total revenues	$ 525,664	$ 501,569	$ 485,452	$ 443,039	$ 525,764	$ 553,210	$ 489,437	$ 438,229	1,955,724	2,006,640	2,033,885
Expenses
Employee costs									566,178	604,353	658,266
Other operating expenses, including $276 each year to affiliates									351,511	363,986	381,954
Depreciation and amortization									25,878	30,044	30,298
Interest									3,458	3,062	2,096
Total expenses									1,880,657	1,918,614	2,024,192
Income before taxes and income (losses) from subsidiaries									75,067	88,026	9,693
Income tax (benefit) expense									14,921	19,605	5,650
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)
Retained earnings at beginning of year				471,788					471,788
Cash paid on Class B Common Shares conversion										(12,000)
Cumulative effect adjustment on adoption of new accounting pronouncement											0
Retained earnings at end of year	491,698				471,788				491,698	471,788
Parent Company
Revenues
Investment income									20,000	20,000	15,000
Other income									784	1,252	922
Total revenues									20,784	21,252	15,922
Expenses
Employee costs									1,388	832	156
Other operating expenses, including $276 each year to affiliates									4,447	6,641	7,617
Depreciation and amortization									5	69	162
Interest									3,123	2,726	1,726
Total expenses									8,963	10,268	9,661
Income before taxes and income (losses) from subsidiaries									11,821	10,984	6,261
Income tax (benefit) expense									(776)	2,928	0
Income (losses) from subsidiaries									36,062	47,422	(12,465)
Net income (loss) attributable to Stewart									48,659	55,478	(6,204)
Retained earnings at beginning of year				$ 471,788				$ 455,519	471,788	455,519	479,733
Cash dividends on Common Stock									(28,749)	(27,840)	(18,010)
Cash paid on Class B Common Shares conversion									0	(12,000)	0
Cumulative effect adjustment on adoption of new accounting pronouncement	0				631				0	631	0
Retained earnings at end of year	$ 491,698				$ 471,788				$ 491,698	$ 471,788	$ 455,519