Segment Information (Schedule of Selected Financial Information) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Revenues	$ 2,555,928	$ 1,913,721	$ 6,848,048	$ 4,935,393
Income (loss) before income taxes	603,174	243,371	1,308,612	540,990
Depreciation and amortization	39,238	38,227	118,475	110,652
Capital expenditures	45,535	35,148	114,122	94,471
Direct premiums and escrow fees	921,336	807,947	2,624,462	2,080,568
Agent premiums	998,534	722,434	2,748,723	1,920,011
Information and other	310,145	285,882	890,476	728,563
Net investment income	50,670	52,466	155,797	156,760
Net realized investment gains (losses)	275,243	44,992	428,590	49,491
Operating Segments
Segment Reporting Information [Line Items]
Revenues	2,279,005	1,908,325	6,474,644	4,927,376
Direct premiums and escrow fees	921,336	807,947	2,624,462	2,080,568
Agent premiums	998,534	722,434	2,748,723	1,920,011
Information and other	310,405	286,121	891,256	729,188
Net investment income	51,509	46,831	145,395	154,633
Net realized investment gains (losses)	(2,779)	44,992	64,808	42,976
Operating Segments | Title Insurance and Services
Segment Reporting Information [Line Items]
Revenues	2,146,779	1,771,993	6,054,309	4,535,558
Income (loss) before income taxes	352,366	337,480	990,585	648,261
Depreciation and amortization	37,792	36,194	113,976	104,705
Capital expenditures	44,570	33,034	111,638	86,456
Direct premiums and escrow fees	794,215	680,910	2,238,956	1,712,946
Agent premiums	998,534	722,434	2,748,723	1,920,011
Information and other	307,616	282,671	881,262	719,196
Net investment income	49,827	44,726	139,963	147,628
Net realized investment gains (losses)	(3,413)	41,252	45,405	35,777
Operating Segments | Specialty Insurance
Segment Reporting Information [Line Items]
Revenues	132,226	136,332	420,335	391,818
Income (loss) before income taxes	(1,887)	(72,129)	24,106	(51,954)
Depreciation and amortization	1,410	1,995	4,392	5,832
Capital expenditures	965	2,114	2,484	8,015
Direct premiums and escrow fees	127,121	127,037	385,506	367,622
Agent premiums	0	0	0	0
Information and other	2,789	3,450	9,994	9,992
Net investment income	1,682	2,105	5,432	7,005
Net realized investment gains (losses)	634	3,740	19,403	7,199
Corporate
Segment Reporting Information [Line Items]
Revenues	277,374	6,055	375,185	9,260
Income (loss) before income taxes	252,695	(21,980)	293,921	(55,317)
Depreciation and amortization	36	38	107	115
Capital expenditures	0	0	0	0
Net realized investment gains (losses)	85,800
Eliminations
Segment Reporting Information [Line Items]
Revenues	(451)	(659)	(1,781)	(1,243)
Income (loss) before income taxes	0	0	0	0
Depreciation and amortization	0	0	0	0
Capital expenditures	$ 0	$ 0	$ 0	$ 0