Consolidated Statements of Earnings and Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Net premiums earned	$ 4,976,190	$ 4,954,990	$ 4,975,777
Net investment income	500,534	451,016	438,455
Change in the fair value of equity securities	(228,994)
Net realized capital gains	(3,241)	107,222	63,205
Other than temporary impairment losses	(1,328)
Other than temporary impairment losses		(16,871)	(45,165)
Total revenues	6,887,160	6,424,655	6,131,019
Costs and Expenses
Net loss and loss adjustment expenses	3,520,431	3,620,197	2,917,166
Commissions, brokerage and other underwriting expenses	1,617,333	1,651,177	1,657,251
Other operating expenses	1,579,309	967,104	765,226
Corporate administration	15,732	46,998	42,960
Amortization of intangible assets	24,039	19,419	19,012
Interest expense	90,724	83,070	81,599
Total costs and expenses	6,847,568	6,387,965	5,483,214
Earnings before income taxes	39,592	36,690	647,805
Income taxes	(15,062)	(63,802)	187,141
Net earnings	54,654	100,492	460,664
Net earnings attributable to noncontrolling interest	15,115	10,359	3,743
Net earnings attributable to Alleghany stockholders	39,539	90,133	456,921
Net earnings	54,654	100,492	460,664
Other comprehensive income (loss):
Change in unrealized gains (losses), net of deferred taxes of ($56,498), $280,526 and $36,468 for 2018, 2017 and 2016, respectively	(212,539)	520,976	67,726
Less: reclassification for net realized capital gains and other than temporary impairments, net of taxes of $3,125, ($25,806) and ($36,281) for 2018, 2017 and 2016, respectively	11,757	(47,925)	(67,380)
Change in unrealized currency translation adjustment, net of deferred taxes of ($5,822), $14,344 and ($3,889) for 2018, 2017 and 2016, respectively	(21,902)	26,639	(7,223)
Retirement plans	3,071	(3,755)	(112)
Comprehensive income (loss)	(164,959)	596,427	453,675
Comprehensive income attributable to noncontrolling interests	15,115	10,359	3,743
Comprehensive income (loss) attributable to Alleghany stockholders	$ (180,074)	$ 586,068	$ 449,932
Basic earnings per share attributable to Alleghany stockholders	$ 2.62	$ 5.85	$ 29.60
Diluted earnings per share attributable to Alleghany stockholders	$ 2.62	$ 5.85	$ 29.59
Noninsurance Revenue
Revenues
Noninsurance revenue	$ 1,643,999	$ 928,298	$ 698,747