Consolidated Statements of Earnings and Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenues
Net premiums earned	$ 1,604,763	$ 1,444,420
Net investment income	153,484	111,982
Change in the fair value of equity securities	112,728	(522,976)
Net realized capital gains	12,931	13,026
Change in allowance for credit losses on available for sale securities	1,972	(31,375)
Noninsurance revenue	767,835	467,849
Total revenues	2,653,713	1,482,926
Costs and Expenses
Net loss and loss adjustment expenses	1,112,070	1,027,444
Commissions, brokerage and other underwriting expenses	476,036	441,396
Other operating expenses	723,889	466,661
Corporate administration	9,558	(14,307)
Amortization of intangible assets	11,478	9,568
Interest expense	23,752	18,356
Total costs and expenses	2,356,783	1,949,118
Earnings (losses) before income taxes	296,930	(466,192)
Income taxes	58,867	(104,720)
Net earnings (losses)	238,063	(361,472)
Net earnings (losses) attributable to noncontrolling interest	8,022	(254)
Net earnings (losses) attributable to Alleghany stockholders	230,041	(361,218)
Net earnings (losses)	238,063	(361,472)
Other comprehensive income (loss):
Change in unrealized gains, net of deferred taxes	(217,935)	(276,629)
Change in unrealized currency translation adjustment, net of deferred taxes	2,461	(13,733)
Retirement plans	(965)	517
Comprehensive income (loss)	9,851	(662,165)
Comprehensive income (loss) attributable to noncontrolling interests	8,022	(254)
Comprehensive income (loss) attributable to Alleghany stockholders	$ 1,829	$ (661,911)
Basic earnings (losses) per share attributable to Alleghany stockholders	$ 16.44	$ (25.19)
Diluted earnings (losses) per share attributable to Alleghany stockholders	$ 16.37	$ (25.37)
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	$ (11,773)	$ (10,848)