Schedule I - Financial Information of the Registrant (Parent Company) - Statements of Income and Retained Earnings (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	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	Jan. 01, 2018	Jan. 01, 2016
Revenues
Investment income									$ 19,737	$ 18,932	$ 18,925
Total revenues	$ 469,934	$ 507,640	$ 492,869	$ 437,229	$ 525,664	$ 501,569	$ 485,452	$ 443,039	1,907,672	1,955,724	2,006,640
Expenses
Interest									3,875	3,458	3,062
Other operating expenses, including $276 each year to affiliates									345,307	351,511	363,986
Total expenses									1,835,143	1,880,657	1,918,614
Income before taxes and income from subsidiaries									72,529	75,067	88,026
Income tax expense (benefit)									13,507	14,921	19,605
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
Retained earnings at beginning of year				491,698					491,698
Cash paid on Class B Common Shares conversion											(12,000)
Cumulative effect adjustments on adoption of new accounting pronouncements												$ 0	$ 0
Retained earnings at end of year	514,248				491,698				514,248	491,698
Parent Company
Revenues
Investment income									25,000	20,000	20,000
Other income									665	784	1,252
Total revenues									25,665	20,784	21,252
Expenses
Interest									3,511	3,123	2,726
Other operating expenses, including $276 each year to affiliates									15,174	5,840	7,542
Total expenses									18,685	8,963	10,268
Income before taxes and income from subsidiaries									6,980	11,821	10,984
Income tax expense (benefit)									126	(776)	2,928
Income from subsidiaries									40,669	36,062	47,422
Net income attributable to Stewart									47,523	48,659	55,478
Retained earnings at beginning of year				$ 491,698				$ 471,788	491,698	471,788	455,519
Cash dividends on Common Stock									(28,565)	(28,749)	(27,840)
Cash paid on Class B Common Shares conversion									0	0	(12,000)
Cumulative effect adjustments on adoption of new accounting pronouncements	3,592				0				3,592	0	631
Retained earnings at end of year	$ 514,248				$ 491,698				$ 514,248	$ 491,698	$ 471,788