Consolidated Statements of Earnings and Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenues
Net premiums earned	$ 1,444,420	$ 1,297,309
Net investment income	111,982	123,049
Change in the fair value of equity securities	(522,976)	392,353
Net realized capital gains	13,026	4,442
Credit losses for available for sale securities	(31,375)
Credit losses for available for sale securities		(10,020)
Noninsurance revenue	467,849	514,123
Total revenues	1,482,926	2,321,256
Costs and Expenses
Net loss and loss adjustment expenses	1,027,444	792,498
Commissions, brokerage and other underwriting expenses	441,396	420,126
Other operating expenses	466,661	502,418
Corporate administration	(14,307)	19,369
Amortization of intangible assets	9,568	6,900
Interest expense	18,356	23,531
Total costs and expenses	1,949,118	1,764,842
(Losses) earnings before income taxes	(466,192)	556,414
Income taxes	(104,720)	108,512
Net (losses) earnings	(361,472)	447,902
Net (losses) earnings attributable to noncontrolling interest	(254)	7,675
Net (losses) earnings attributable to Alleghany stockholders	(361,218)	440,227
Net (losses) earnings	(361,472)	447,902
Other comprehensive income (loss):
Change in unrealized gains, net of deferred taxes	(276,629)	183,387
Less: reclassification for net realized capital gains and credit losses for available for sale securities, net of taxes	(10,848)	4,407
Change in unrealized currency translation adjustment, net of deferred taxes	(13,733)	(885)
Retirement plans	517	937
Comprehensive (loss) income	(662,165)	635,748
Comprehensive (loss) income attributable to noncontrolling interests	(254)	7,675
Comprehensive (loss) income attributable to Alleghany stockholders	$ (661,911)	$ 628,073
Basic (losses) earnings per share attributable to Alleghany stockholders	$ (25.19)	$ 30.40
Diluted (losses) earnings per share attributable to Alleghany stockholders	$ (25.37)	$ 30.39