Consolidated Statements of Earnings and Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenues
Net premiums earned	$ 1,389,981	$ 1,225,346	$ 4,043,298	$ 3,670,161
Net investment income	147,829	127,329	413,623	377,728
Change in the fair value of equity securities	(16,691)	370,175	519,322	512,771
Net realized capital gains	3,957	16,230	20,753	67,197
Other than temporary impairment losses	(3,597)	(3)	(13,617)	(514)
Noninsurance revenue	638,478	438,338	1,756,507	1,032,690
Total revenues	2,159,957	2,177,415	6,739,886	5,660,033
Costs and Expenses
Net loss and loss adjustment expenses	907,736	957,703	2,497,037	2,366,491
Commissions, brokerage and other underwriting expenses	449,519	407,679	1,313,961	1,216,057
Other operating expenses	617,326	415,378	1,701,218	1,023,440
Corporate administration	22,276	19,094	67,612	40,998
Amortization of intangible assets	8,095	5,500	23,790	16,730
Interest expense	25,703	22,189	74,363	65,997
Total costs and expenses	2,030,655	1,827,543	5,677,981	4,729,713
Earnings before income taxes	129,302	349,872	1,061,905	930,320
Income taxes	28,010	60,413	207,878	171,275
Net earnings	101,292	289,459	854,027	759,045
Net earnings attributable to noncontrolling interest	10,860	4,559	27,909	7,454
Net earnings attributable to Alleghany stockholders	90,432	284,900	826,118	751,591
Net earnings	101,292	289,459	854,027	759,045
Other comprehensive income (loss):
Change in unrealized gains (losses), net of deferred taxes	86,215	(33,601)	442,205	(213,263)
Less: reclassification for net realized capital gains and other than temporary impairments, net of taxes	(4,892)	(12,819)	(10,246)	(16,546)
Change in unrealized currency translation adjustment, net of deferred taxes	(10,343)	(1,530)	(8,054)	(6,953)
Retirement plans	322	(551)	1,363	(1,664)
Comprehensive income	172,594	240,958	1,279,295	520,619
Comprehensive income attributable to noncontrolling interests	10,860	4,559	27,909	7,454
Comprehensive income attributable to Alleghany stockholders	$ 161,734	$ 236,399	$ 1,251,386	$ 513,165
Basic earnings per share attributable to Alleghany stockholders	$ 6.27	$ 19.07	$ 57.18	$ 49.55
Diluted earnings per share attributable to Alleghany stockholders	$ 6.27	$ 19.07	$ 57.14	$ 49.53