Schedule II - Condensed Financial Information of Registrant - Condensed Statements of Operations (Detail) - USD ($)	3 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	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Premiums and other revenues
Net investment income									$ 1,077,406,000	$ 858,367,000	$ 966,077,000
Net realized investment gains (losses)									37,719,000	18,174,000
Net realized investment gains (losses)											104,595,000
Other-than-temporary impairments									(6,968,000)	(1,243,000)	(13,386,000)
Net gains (losses) on equity securities									422,535,000	(107,188,000)	0
Other income									51,401,000	44,530,000	37,986,000
Total premiums and other revenues	$ 1,057,273,000	$ 932,500,000	$ 956,677,000	$ 1,123,693,000	$ 518,700,000	$ 1,052,236,000	$ 952,071,000	$ 803,375,000	4,070,143,000	3,326,382,000	3,411,000,000
BENEFITS, LOSSES AND EXPENSES
Other operating expenses									524,888,000	497,011,000	485,340,000
Total benefits, losses and expenses	835,864,000	848,134,000	852,773,000	838,995,000	682,868,000	868,969,000	850,796,000	782,591,000	3,375,766,000	3,185,224,000	3,082,654,000
Income before federal income tax and other items	221,409,000	84,366,000	103,904,000	284,698,000	(164,168,000)	183,267,000	101,275,000	20,784,000	694,377,000	141,158,000	328,346,000
Provision (benefit) for federal income taxes	53,617,000	22,475,000	21,948,000	67,377,000	(40,920,000)	19,219,000	21,957,000	1,189,000	165,417,000	1,445,000	(92,995,000)
Equity in earnings of unconsolidated affiliates	1,176,000	45,075,000	16,790,000	40,460,000	2,376,000	13,029,000	6,421,000	(545,000)	103,501,000	21,281,000	86,674,000
Other components of net periodic pension costs, net of tax	2,124,000	(1,023,000)	(871,000)	(914,000)	3,133,000	(1,236,000)	(1,677,000)	(792,000)	(684,000)	(572,000)	(12,408,000)
Net income attributable to American National	$ 171,122,000	$ 92,184,000	$ 98,840,000	$ 258,217,000	$ (117,385,000)	$ 173,464,000	$ 84,139,000	$ 18,777,000	620,363,000	158,995,000	493,651,000
Parent Company
Premiums and other revenues
Premiums and other policy revenues									873,076,000	943,071,000	889,346,000
Net investment income									866,837,000	686,569,000	794,277,000
Net realized investment gains (losses)									5,600,000	2,053,000	21,052,000
Net realized investment gains (losses)											21,052,000
Other-than-temporary impairments									(6,663,000)	(1,243,000)	(6,105,000)
Net gains (losses) on equity securities									958,000	(208,000)	0
Other income									28,037,000	19,028,000	17,558,000
Total premiums and other revenues									1,767,845,000	1,649,270,000	1,716,128,000
BENEFITS, LOSSES AND EXPENSES
Policyholder benefits									651,162,000	716,959,000	682,707,000
Other operating expenses									965,338,000	773,329,000	871,935,000
Total benefits, losses and expenses									1,616,500,000	1,490,288,000	1,554,642,000
Income before federal income tax and other items									151,345,000	158,982,000	161,486,000
Provision (benefit) for federal income taxes									27,568,000	28,308,000	(53,728,000)
Equity in earnings of unconsolidated affiliates									492,888,000	24,789,000	286,579,000
Other components of net periodic pension costs, net of tax									3,698,000	3,532,000	(8,142,000)
Net income attributable to American National									$ 620,363,000	$ 158,995,000	$ 493,651,000