Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands		12 Months Ended
	Mar. 15, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities
Net earnings		$ 890,201	$ 54,654	$ 100,492
Adjustments to reconcile net earnings to net cash provided by (used in) operating activities:
Depreciation and amortization		119,513	127,374	135,029
Change in the fair value of equity securities		(709,695)	228,994
Net realized capital (gains) losses		6,551	3,241	(107,222)
Other than temporary impairment losses		19,660	1,328
Other than temporary impairment losses				16,871
Net adjustments		(175,796)	347,769	345,243
Net cash provided by (used in) operating activities		714,405	402,423	445,735
Cash flows from investing activities
Purchases of equity securities		(520,961)	(1,041,887)
Purchases of equity securities				(4,574,415)
Purchases of debt securities		(6,726,809)	(4,716,070)	(5,805,364)
Sales of debt securities		3,645,307	3,647,156	3,986,259
Maturities and redemptions of debt securities		1,166,841	1,526,060	1,943,263
Sales of equity securities		2,296,371	1,609,647
Sales of equity securities				4,315,408
Net (purchase) sale of short-term investments		(21,564)	(316,366)	145,237
Purchases of property and equipment		(47,572)	(23,286)	6,775
Other, net		(40,218)	(86,478)	(22,678)
Net cash provided by (used in) investing activities		(476,539)	345,432	(155,120)
Cash flows from financing activities
Treasury stock acquisitions		(144,422)	(491,633)	(16,048)
Cash dividends paid	$ (154,000)		(153,967)
Other, net		(40,530)	4,512	(19,400)
Net cash provided by (used in) financing activities		(103,214)	(536,684)	(64,372)
Net increase (decrease) in cash		140,335	200,388	244,284
Cash at beginning of period		1,038,763	838,375	594,091
Cash at end of period		1,179,098	1,038,763	838,375
Cash paid during the period for:
Interest paid		97,016	88,345	83,171
Income taxes paid (refunds received)		61,786	33,677	8,863
Parent Company
Cash flows from operating activities
Net earnings		890,201	54,654	100,492
Adjustments to reconcile net earnings to net cash provided by (used in) operating activities:
Equity in undistributed net (earnings) losses of consolidated subsidiaries		(989,486)	(130,050)	(154,577)
Depreciation and amortization		2,249	1,750	1,916
Change in the fair value of equity securities		(3,937)	44,780
Net realized capital (gains) losses		13,497	265	(3,326)
Increase (decrease) in other liabilities and taxes payable		24,593	(84,803)	25,040
Net adjustments		(953,084)	(168,058)	(130,947)
Net cash provided by (used in) operating activities		(62,883)	(113,404)	(30,455)
Cash flows from investing activities
Purchases of equity securities			(31,125)
Purchases of equity securities				(1,427,194)
Purchases of debt securities		(194,706)	(3,418)
Sales of debt securities		1,186	29,189	4,909
Maturities and redemptions of debt securities		13,344	53	73
Sales of equity securities		64,016	360,579
Sales of equity securities				1,213,974
Net (purchase) sale of short-term investments		162,161	(195,983)	143,920
Purchases of property and equipment		(124)		(76)
Other, net		(33,245)	(4,926)	(35,182)
Net cash provided by (used in) investing activities		12,632	154,369	(99,576)
Cash flows from financing activities
Treasury stock acquisitions		(144,422)	(491,633)	(16,048)
Cash dividends paid			(153,967)
Capital contributions to consolidated subsidiaries		(15,267)	(175,653)	(245,000)
Distributions from consolidated subsidiaries		215,000	751,471	405,000
Other, net		(4,707)	7,868	1,220
Net cash provided by (used in) financing activities		50,604	(61,914)	145,172
Net increase (decrease) in cash		353	(20,949)	15,141
Cash at beginning of period		331	21,280	6,139
Cash at end of period		684	331	21,280
Cash paid during the period for:
Interest paid		51,375	51,375	51,375
Income taxes paid (refunds received)		$ (4,189)	$ (8,338)	$ 8,140