Consolidated Statements of Earnings and Comprehensive Income - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenues
Net premiums earned		$ 7,097,653	$ 6,000,161	$ 5,478,143
Net investment income		540,445	490,856	550,241
Change in the fair value of equity securities		506,769	(110,459)	709,695
Net realized capital gains		67,493	3,098	(6,551)
Change in allowance for credit losses on available for sale securities		2,077	(8,029)
Change in allowance for credit losses on available for sale securities				(19,660)
Product and service revenues		3,789,668	2,521,092	2,328,848
Total revenues		12,004,105	8,896,719	9,040,716
Costs and Expenses
Net loss and loss adjustment expenses		4,834,935	4,339,046	3,686,435
Commissions, brokerage and other underwriting expenses	[1]	2,067,501	1,789,820	1,758,698
Other operating expenses		3,479,528	2,429,262	2,263,326
Corporate administration		57,218	48,581	74,830
Amortization of intangible assets		49,912	44,241	33,834
Interest expense		102,308	88,152	99,957
Total costs and expenses		10,591,402	8,739,102	7,917,080
Earnings (losses) before income taxes		1,412,703	157,617	1,123,636
Income taxes		281,925	30,734	233,435
Net earnings		1,130,778	126,883	890,201
Net earnings attributable to noncontrolling interest		95,886	25,129	32,400
Net earnings attributable to Alleghany stockholders		1,034,892	101,754	857,801
Net earnings		1,130,778	126,883	890,201
Other comprehensive income (loss):
Change in unrealized gains (losses), net of deferred taxes		(253,301)	277,040	402,957
Change in unrealized currency translation adjustment, net of deferred taxes		(4,305)	22,366	2,933
Retirement plans		(463)	14,754	(12,153)
Comprehensive income		820,198	407,935	1,263,554
Comprehensive income attributable to noncontrolling interests		95,886	25,129	32,400
Comprehensive income attributable to Alleghany stockholders		$ 724,312	$ 382,806	$ 1,231,154
Basic earnings per share attributable to Alleghany stockholders		$ 74.70	$ 7.14	$ 59.44
Diluted earnings per share attributable to Alleghany stockholders		$ 74.66	$ 7.04	$ 59.39
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		$ (52,511)	$ (33,108)	$ (20,384)

[1] Includes amortization associated with deferred acquisition costs of $1,693.1 million, $1,457.0 million and $1,392.8 million for the years ended December 31, 2021, 2020 and 2019, respectively.