Consolidated Statements of Earnings and Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues
Net premiums earned	$ 1,556,859	$ 1,389,981	$ 4,396,147	$ 4,043,298
Net investment income	129,265	147,829	359,938	413,623
Change in the fair value of equity securities	92,799	(16,691)	(187,991)	519,322
Net realized capital gains	16,751	3,957	(8,323)	20,753
Change in allowance for credit losses on available for sale securities	3,454		(10,900)
Change in allowance for credit losses on available for sale securities		(3,597)		(13,617)
Noninsurance revenue	723,785	638,478	1,684,335	1,756,507
Total revenues	2,522,913	2,159,957	6,233,206	6,739,886
Costs and Expenses
Net loss and loss adjustment expenses	1,173,655	907,736	3,225,461	2,497,037
Commissions, brokerage and other underwriting expenses	464,522	449,519	1,315,935	1,313,961
Other operating expenses	669,423	617,326	1,646,390	1,701,218
Corporate administration	12,871	22,276	17,143	67,612
Amortization of intangible assets	11,223	8,095	32,884	23,790
Interest expense	23,319	25,703	63,869	74,363
Total costs and expenses	2,355,013	2,030,655	6,301,682	5,677,981
(Losses) earnings before income taxes	167,900	129,302	(68,476)	1,061,905
Income taxes	30,253	28,010	(21,111)	207,878
Net (losses) earnings	137,647	101,292	(47,365)	854,027
Net earnings attributable to noncontrolling interest	11,125	10,860	9,953	27,909
Net (losses) earnings attributable to Alleghany stockholders	126,522	90,432	(57,318)	826,118
Net (losses) earnings	137,647	101,292	(47,365)	854,027
Other comprehensive income (loss):
Change in unrealized gains, net of deferred taxes	77,133	86,215	212,175	442,205
Less: reclassification for net realized capital gains and change in allowance for credit losses on available for sale securities, net of taxes	(6,345)	(4,892)	(22,761)	(10,246)
Change in unrealized currency translation adjustment, net of deferred taxes	12,109	(10,343)	13,190	(8,054)
Retirement plans	420	322	1,356	1,363
Comprehensive (loss) income	220,964	172,594	156,595	1,279,295
Comprehensive (loss) income attributable to noncontrolling interests	11,125	10,860	9,953	27,909
Comprehensive (loss) income attributable to Alleghany stockholders	$ 209,839	$ 161,734	$ 146,642	$ 1,251,386
Basic (losses) earnings per share attributable to Alleghany stockholders	$ 8.86	$ 6.27	$ (4.01)	$ 57.18
Diluted (losses) earnings per share attributable to Alleghany stockholders	$ 8.86	$ 6.27	$ (4.43)	$ 57.14