Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Revenues
Net premiums earned	$ 9,678,077	$ 8,082,298	$ 6,991,935
Net investment income	496,547	389,118	519,608
Net realized gains (losses)	(662,734)	379,845	823,460
Other underwriting income	13,227	22,073	26,784
Equity in net income of investments accounted for using the equity method	115,856	366,402	146,693
Other income (loss)	(26,165)	10,244	29
Total revenues	9,614,808	9,249,980	8,508,509
Expenses
Losses and loss adjustment expenses	5,027,517	4,584,803	4,689,599
Acquisition expenses	1,739,580	1,303,178	1,004,842
Other operating expenses	1,128,175	998,595	875,176
Corporate expenses	95,482	79,157	81,988
Amortization of intangible assets	106,200	82,955	69,031
Interest expense	130,266	139,470	143,456
Net foreign exchange losses (gains)	(100,905)	(41,529)	83,634
Total expenses	8,126,315	7,146,629	6,947,726
Income before income taxes and income (loss) from operating affiliates	1,488,493	2,103,351	1,560,783
Income taxes:
Current tax expense (benefit)	201,216	295,533	197,662
Deferred tax expense (benefit)	(121,255)	(166,951)	(85,824)
Income tax expense	79,961	128,582	111,838
Income (loss) from operating affiliates	73,891	264,693	16,766
Net income	1,482,423	2,239,462	1,465,711
Net (income) loss attributable to noncontrolling interests	(5,490)	(82,613)	(60,190)
Net income available to Arch	1,476,933	2,156,849	1,405,521
Preferred share dividends	(40,736)	(48,343)	(41,612)
Loss on redemption of preferred shares	0	(15,101)	0
Net income available to Arch common shareholders	$ 1,436,197	$ 2,093,405	$ 1,363,909
Net income per common share and common share equivalent
Basic (per share)	$ 3.90	$ 5.34	$ 3.38
Diluted (per share)	$ 3.80	$ 5.23	$ 3.32
Weighted average common shares and common share equivalents outstanding
Basic (shares)	368,612,197	391,748,715	403,062,179
Diluted (shares)	377,609,767	400,345,936	410,259,455