Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands		12 Months Ended
	Mar. 15, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities
Net earnings		$ 54,654	$ 100,492	$ 460,664
Adjustments to reconcile net earnings to net cash provided by (used in) operating activities:
Depreciation and amortization		127,374	135,029	160,469
Change in the fair value of equity securities		228,994
Net realized capital (gains) losses		3,241	(107,222)	(63,205)
Other than temporary impairment losses		1,328
Net adjustments		347,769	345,243	332,263
Net cash (used in) provided by operating activities		402,423	445,735	792,927
Cash flows from investing activities
Purchases of equity securities			(4,574,415)	(2,093,644)
Purchases of equity securities		(1,041,887)
Purchases of debt securities		(4,716,070)	(5,805,364)	(5,960,516)
Sales of debt securities		3,647,156	3,986,259	4,895,282
Maturities and redemptions of debt securities		1,526,060	1,943,263	1,512,879
Sales of equity securities			4,315,408	2,067,095
Sales of equity securities		1,609,647
Net (purchase) sale of short-term investments		(316,366)	145,237	(442,784)
Purchases of property and equipment		(23,286)	6,775	(24,005)
Other, net		(86,478)	(22,678)	(29,861)
Net cash provided by (used in) investing activities		345,432	(155,120)	(672,727)
Cash flows from financing activities
Treasury stock acquisitions		(491,633)	(16,048)	(68,320)
Cash dividends paid	$ (154,000)	(153,967)
Other, net		4,512	(19,400)	(6,007)
Net cash provided by (used in) financing activities		(536,684)	(64,372)	(17,414)
Net increase (decrease) in cash		200,388	244,284	118,824
Cash at beginning of period		838,375	594,091	475,267
Cash at end of period		1,038,763	838,375	594,091
Cash paid during the period for:
Interest paid		88,345	83,171	80,817
Income taxes paid (refunds received)		39,677	8,863	83,023
Parent Company
Cash flows from operating activities
Net earnings		54,654	100,492	460,664
Adjustments to reconcile net earnings to net cash provided by (used in) operating activities:
Equity in undistributed net (earnings) losses of consolidated subsidiaries		(130,050)	(154,577)	(524,201)
Depreciation and amortization		1,750	1,916	2,035
Change in the fair value of equity securities		44,780	0	0
Net realized capital (gains) losses		265	(3,326)	10,674
Other than temporary impairment losses		0	0	0
Increase (decrease) in other liabilities and taxes payable		(84,803)	25,040	14,677
Net adjustments		(168,058)	(130,947)	(496,815)
Net cash (used in) provided by operating activities		(113,404)	(30,455)	(36,151)
Cash flows from investing activities
Purchases of equity securities			(1,427,194)	(132,129)
Purchases of equity securities		(31,125)	0	0
Purchases of debt securities		(3,418)		0
Sales of debt securities		29,189	4,909
Maturities and redemptions of debt securities		53	73	73
Sales of equity securities			1,213,974	166,634
Sales of equity securities		360,579
Net (purchase) sale of short-term investments		(195,983)	143,920	(152,375)
Purchases of property and equipment		0	(76)	(5,779)
Other, net		(4,926)	(35,182)	(37,600)
Net cash provided by (used in) investing activities		154,369	(99,576)	(161,176)
Cash flows from financing activities
Treasury stock acquisitions		(491,633)	(16,048)	(68,320)
Cash dividends paid		(153,967)	0	0
Capital contributions to consolidated subsidiaries		(175,653)	(245,000)	(163,732)
Distributions from consolidated subsidiaries		751,471	405,000	434,900
Other, net		7,868	1,220	(1,859)
Net cash provided by (used in) financing activities		(61,914)	145,172	200,989
Net increase (decrease) in cash		(20,949)	15,141	3,662
Cash at beginning of period		21,280	6,139	2,477
Cash at end of period		331	21,280	6,139
Cash paid during the period for:
Interest paid		51,375	51,375	51,375
Income taxes paid (refunds received)		$ (8,338)	$ 8,140	$ 37,220