Unaudited Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues
Net premiums written	$ 1,325,403	$ 1,014,278	$ 3,850,358	$ 3,159,076
Change in unearned premiums	(63,517)	(55,875)	(230,581)	(243,109)
Net premiums earned	1,261,886	958,403	3,619,777	2,915,967
Net investment income	116,459	93,618	345,457	275,691
Net realized gains (losses)	66,275	125,105	122,163	230,647
Other-than-temporary impairment losses	(1,878)	(3,867)	(5,415)	(16,999)
Less investment impairments recognized in other comprehensive income, before taxes	0	0	0	150
Net impairment losses recognized in earnings	(1,878)	(3,867)	(5,415)	(16,849)
Other underwriting income	6,064	7,980	15,519	38,251
Equity in net income (loss) of investment funds accounted for using the equity method	31,090	16,662	111,884	32,054
Other income (loss)	(342)	(400)	(3,118)	(432)
Total revenues	1,479,554	1,197,501	4,206,267	3,475,329
Expenses
Losses and loss adjustment expenses	1,046,141	524,183	2,288,571	1,631,724
Acquisition expenses	193,854	161,267	566,579	501,782
Other operating expenses	170,127	153,286	514,827	460,748
Corporate expenses	17,098	18,485	69,766	45,068
Amortization of intangible assets	31,824	4,865	93,942	14,493
Interest expense	29,510	15,943	86,935	47,713
Net foreign exchange losses (gains)	28,028	2,621	86,975	1,525
Total expenses	1,516,582	880,650	3,707,595	2,703,053
Income (loss) before income taxes	(37,028)	316,851	498,672	772,276
Income tax expense	(8,189)	(13,231)	(70,755)	(43,672)
Net income (loss)	(45,217)	303,620	427,917	728,604
Net (income) loss attributable to noncontrolling interests	11,561	(50,748)	(23,279)	(109,879)
Net income (loss) available to Arch	(33,656)	252,872	404,638	618,725
Preferred dividends	(12,369)	(5,484)	(34,936)	(16,453)
Loss on redemption of preferred shares	(6,735)	0	(6,735)	0
Net income (loss) available to Arch common shareholders	$ (52,760)	$ 247,388	$ 362,967	$ 602,272
Net income per common share
Basic (per share)	$ (0.39)	$ 2.05	$ 2.70	$ 4.99
Diluted (per share)	$ (0.39)	$ 1.98	$ 2.61	$ 4.84
Weighted average common shares and common share equivalents outstanding
Basic (shares)	134,885,451	120,938,916	134,472,129	120,656,420
Diluted (shares)	134,885,451	124,931,653	139,222,324	124,528,174