Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock	Noncontrolling Interest
Balance at beginning of the period at Dec. 31, 2017	$ 5,255,771	$ 30,832	$ 19,193	$ 642,216	$ 4,656,134	$ (101,616)	$ 9,012
Stockholders' Equity [Roll Forward]
Reissuance of treasury shares	745		675			70
Amortization of restricted stock	201		201
Cumulative effect of accounting change	59,931			(637,376)	697,307
Other comprehensive income (loss)	(90,910)			(90,910)
Net income attributable to American National	18,777				18,777
Cash dividends to common stockholders	(22,089)				(22,089)
Distributions	(397)						(397)
Net loss attributable to noncontrolling interest	(519)						(519)
Balance at end of the period at Mar. 31, 2018	5,221,510	30,832	20,069	(86,070)	5,350,129	(101,546)	8,096
Balance at beginning of the period at Dec. 31, 2017	5,255,771	30,832	19,193	642,216	4,656,134	(101,616)	9,012
Stockholders' Equity [Roll Forward]
Other comprehensive income (loss)	(138,806)
Net income attributable to American National	276,380
Balance at end of the period at Sep. 30, 2018	5,381,670	30,832	20,673	(123,709)	5,553,383	(108,492)	8,983
Balance at beginning of the period at Mar. 31, 2018	5,221,510	30,832	20,069	(86,070)	5,350,129	(101,546)	8,096
Stockholders' Equity [Roll Forward]
Reissuance of treasury shares	(6,448)		498			(6,946)
Amortization of restricted stock	83		83
Cumulative effect of accounting change	0			10,257	(10,257)
Other comprehensive income (loss)	(34,921)			(34,921)
Net income attributable to American National	84,139				84,139
Cash dividends to common stockholders	(22,046)				(22,046)
Distributions	(173)						(173)
Net loss attributable to noncontrolling interest	(77)						(77)
Balance at end of the period at Jun. 30, 2018	5,242,067	30,832	20,650	(110,734)	5,401,965	(108,492)	7,846
Stockholders' Equity [Roll Forward]
Amortization of restricted stock	23		23
Other comprehensive income (loss)	(12,975)			(12,975)
Net income attributable to American National	173,464				173,464
Cash dividends to common stockholders	(22,046)				(22,046)
Distributions	(1,240)						(1,240)
Net loss attributable to noncontrolling interest	2,377						2,377
Balance at end of the period at Sep. 30, 2018	5,381,670	30,832	20,673	(123,709)	5,553,383	(108,492)	8,983
Balance at beginning of the period at Dec. 31, 2018	5,271,515	30,832	20,694	(99,738)	5,413,952	(108,492)	14,267
Stockholders' Equity [Roll Forward]
Reissuance of treasury shares	260		237			23
Amortization of restricted stock	20		20
Cumulative effect of accounting change	0			(785)	785
Other comprehensive income (loss)	86,774			86,774
Net income attributable to American National	258,217				258,217
Cash dividends to common stockholders	(22,101)				(22,101)
Contributions	3						3
Distributions	(419)						(419)
Net loss attributable to noncontrolling interest	(1,350)						(1,350)
Balance at end of the period at Mar. 31, 2019	5,592,919	30,832	20,951	(13,749)	5,650,853	(108,469)	12,501
Balance at beginning of the period at Dec. 31, 2018	5,271,515	30,832	20,694	(99,738)	5,413,952	(108,492)	14,267
Stockholders' Equity [Roll Forward]
Other comprehensive income (loss)	185,967
Net income attributable to American National	449,241
Balance at end of the period at Sep. 30, 2019	5,831,708	30,832	20,991	85,444	5,797,783	(108,469)	5,127
Balance at beginning of the period at Mar. 31, 2019	5,592,919	30,832	20,951	(13,749)	5,650,853	(108,469)	12,501
Stockholders' Equity [Roll Forward]
Amortization of restricted stock	20		20
Other comprehensive income (loss)	100,601			100,601
Net income attributable to American National	98,840				98,840
Cash dividends to common stockholders	(22,044)				(22,044)
Contributions	168						168
Distributions	(1,957)						(1,957)
Net loss attributable to noncontrolling interest	(965)						(965)
Balance at end of the period at Jun. 30, 2019	5,767,582	30,832	20,971	86,852	5,727,649	(108,469)	9,747
Stockholders' Equity [Roll Forward]
Amortization of restricted stock	20		20
Other comprehensive income (loss)	(1,408)			(1,408)
Net income attributable to American National	92,184				92,184
Cash dividends to common stockholders	(22,050)				(22,050)
Contributions	56						56
Distributions	(18,435)						(18,435)
Net loss attributable to noncontrolling interest	13,759						13,759
Balance at end of the period at Sep. 30, 2019	$ 5,831,708	$ 30,832	$ 20,991	$ 85,444	$ 5,797,783	$ (108,469)	$ 5,127