Schedule I - Financial Information of the Registrant (Parent Company) - Statements of Income and Retained Earnings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues
Investment income	$ 18,607	$ 19,795	$ 19,737
Merger termination fee	50,000	50,000
Revenues	2,288,432	1,940,008	1,907,672
Expenses
Interest	2,624	4,341	3,875
Other operating expenses	375,188	345,349	345,307
Total expenses	2,069,927	1,823,041	1,835,143
Income before taxes and income from subsidiaries	218,505	116,967	72,529
Income tax expense	(48,833)	(26,695)	(13,507)
Net income attributable to Stewart	154,905	78,615	47,523
Retained Earnings [Roll Forward]
Retained earnings at beginning of year	564,392
Retained earnings at end of year	688,819	564,392
Parent company
Revenues
Investment income	30,000	0	25,000
Merger termination fee	0	50,000	0
Other income	1,182	753	665
Revenues	31,182	50,753	25,665
Expenses
Interest	2,511	4,106	3,511
Other operating expenses	9,262	12,787	15,174
Total expenses	11,773	16,893	18,685
Income before taxes and income from subsidiaries	19,409	33,860	6,980
Income tax expense	(15)	(15)	(126)
Income from subsidiaries	135,511	44,770	40,669
Net income attributable to Stewart	154,905	78,615	47,523
Retained Earnings [Roll Forward]
Retained earnings at beginning of year	564,392	514,248	491,698
Cash dividends on Common Stock	(30,478)	(28,471)	(28,565)
Retained earnings at end of year	688,819	564,392	514,248
Parent company | Cumulative effect adjustments on adoption of new accounting standards (Note 1-H and Note 7)
Retained Earnings [Roll Forward]
Retained earnings at beginning of year	$ 0	0	3,592
Retained earnings at end of year		$ 0	$ 0