Unaudited Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenues
Net premiums written	$ 1,668,311	$ 1,444,898	$ 3,805,557	$ 2,970,157
Change in unearned premiums	(2,957)	18,829	(395,759)	(137,564)
Net premiums earned	1,665,354	1,463,727	3,409,798	2,832,593
Net investment income	131,485	155,038	276,638	311,987
Net realized gains (losses)	556,588	120,757	189,628	261,013
Other underwriting income	6,667	5,953	13,519	14,778
Equity in net income (loss) of investment funds accounted for using the equity method	(65,119)	32,536	(69,328)	79,403
Other income (loss)	(3,140)	1,129	5,408	2,212
Total revenues	2,291,835	1,779,140	3,825,663	3,501,986
Expenses
Losses and loss adjustment expenses	1,230,522	767,543	2,345,941	1,486,075
Acquisition expenses	254,789	210,089	502,072	407,937
Other operating expenses	209,249	198,914	443,793	400,077
Corporate expenses	17,920	18,251	38,716	36,213
Amortization of intangible assets	16,489	19,794	33,120	40,211
Interest expense	31,139	29,280	63,694	58,345
Net foreign exchange (gains) losses	39,211	4,952	(33,460)	1,427
Total expenses	1,799,319	1,248,823	3,393,876	2,430,285
Income (loss) before income taxes	492,516	530,317	431,787	1,071,701
Income tax expense	(26,127)	(44,472)	(54,072)	(90,358)
Net income (loss)	466,389	485,845	377,715	981,343
Net (income) loss attributable to noncontrolling interests	(167,568)	(16,891)	65,223	(63,861)
Net income (loss) available to Arch	298,821	468,954	442,938	917,482
Preferred dividends	(10,403)	(10,403)	(20,806)	(20,806)
Net income (loss) available to Arch common shareholders	$ 288,418	$ 458,551	$ 422,132	$ 896,676
Net income per common share and common share equivalent
Basic (per share)	$ 0.72	$ 1.14	$ 1.05	$ 2.24
Diluted (per share)	$ 0.71	$ 1.12	$ 1.03	$ 2.19
Weighted average common shares and common share equivalents outstanding
Basic (shares)	402,503,687	401,482,784	403,197,924	400,837,181
Diluted (shares)	408,119,681	410,899,483	411,005,591	409,755,250