Schedule I - Financial Information of the Registrant (Parent Company) - Statements of Income and Retained Earnings (Details) - USD ($) $ in Thousands	3 Months Ended								9 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	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	Jan. 01, 2018	Jan. 01, 2017
Revenues
Merger termination fee									$ 50,000	$ 50,000
Investment income										19,795	$ 19,737	$ 18,932
Revenues	$ 509,906	$ 559,508	$ 472,075	$ 398,519	$ 469,934	$ 507,640	$ 492,869	$ 437,229		1,940,008	1,907,672	1,955,724
Expenses
Interest										4,341	3,875	3,458
Other operating expenses, including $276 each year to affiliates										345,349	345,307	351,511
Total expenses										1,823,041	1,835,143	1,880,657
Income before taxes and income from subsidiaries										116,967	72,529	75,067
Income tax (expense) benefit										(26,695)	(13,507)	(14,921)
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
Retained Earnings [Roll Forward]
Retained earnings at beginning of year				514,248					514,248	514,248
Cumulative effect adjustments on adoption of new accounting pronouncements														$ 0
Retained earnings at end of year	564,392				514,248					564,392	514,248
Parent Company
Revenues
Merger termination fee										50,000	0	0
Investment income										0	25,000	20,000
Other income										753	665	784
Revenues										50,753	25,665	20,784
Expenses
Interest										4,106	3,511	3,123
Other operating expenses, including $276 each year to affiliates										12,787	15,174	5,840
Total expenses										16,893	18,685	8,963
Income before taxes and income from subsidiaries										33,860	6,980	11,821
Income tax (expense) benefit										(15)	(126)	776
Income from subsidiaries										44,770	40,669	36,062
Net income attributable to Stewart										78,615	47,523	48,659
Retained Earnings [Roll Forward]
Retained earnings at beginning of year				$ 514,248				$ 491,698	$ 514,248	514,248	491,698	471,788
Cash dividends on Common Stock										(28,471)	(28,565)	(28,749)
Cumulative effect adjustments on adoption of new accounting pronouncements													$ 0	$ 3,592	$ 0
Retained earnings at end of year	$ 564,392				$ 514,248					$ 564,392	$ 514,248	$ 491,698