Consolidated Statements of Earnings and Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Revenues
Net premiums earned	$ 1,715,188	$ 1,784,351	$ 3,320,646	$ 3,389,114
Net investment income	105,452	126,931	218,928	280,415
Change in the fair value of equity securities	(500,223)	203,902	(639,000)	316,630
Net realized capital gains	11,167	12,942	1,164	25,873
Change in allowance for credit losses on available for sale securities	(7,595)	246	(8,177)	2,218
Product and service revenues	1,272,902	800,425	2,422,064	1,568,260
Total revenues	2,596,891	2,928,797	5,315,625	5,582,510
Costs and Expenses
Net loss and loss adjustment expenses	1,039,127	1,087,206	1,980,914	2,199,276
Commissions, brokerage and other underwriting expenses	510,935	523,513	988,100	999,549
Other operating expenses	1,149,986	739,592	2,178,878	1,463,481
Corporate administration	17,278	20,148	28,001	29,706
Amortization of intangible assets	14,941	12,431	29,023	23,909
Interest expense	28,544	24,037	60,654	47,789
Total costs and expenses	2,760,811	2,406,927	5,265,570	4,763,710
(Losses) earnings before income taxes	(163,920)	521,870	50,055	818,800
Income taxes	(40,033)	102,281	5,049	161,148
Net (losses) earnings	(123,887)	419,589	45,006	657,652
Net earnings attributable to noncontrolling interest	47,727	15,938	90,939	23,960
Net (losses) earnings attributable to Alleghany stockholders	(171,614)	403,651	(45,933)	633,692
Net earnings	(123,887)	419,589	45,006	657,652
Other comprehensive income (loss):
Change in unrealized gains, net of deferred taxes	(471,401)	91,560	(1,085,652)	(126,375)
Change in unrealized currency translation adjustment, net of deferred taxes	(25,707)	(2,249)	(26,230)	213
Retirement plans	109	113	239	(852)
Comprehensive (loss) income	(623,708)	498,594	(1,061,097)	508,446
Comprehensive income attributable to noncontrolling interests	47,727	15,938	90,939	23,960
Comprehensive (loss) income attributable to Alleghany stockholders	$ (671,435)	$ 482,656	$ (1,152,036)	$ 484,486
Basic (losses) earnings per share attributable to Alleghany stockholders	$ (12.75)	$ 29.00	$ (3.41)	$ 45.41
Diluted (losses) earnings per share attributable to Alleghany stockholders	$ (12.75)	$ 29.00	$ (3.41)	$ 45.41
Accumulated Net Unrealized Investment Gain Loss
Other comprehensive income (loss):
Less: reclassification for net realized capital gains and change in allowance for credit losses on available for sale securities, net of taxes	$ (2,822)	$ (10,419)	$ 5,540	$ (22,192)