Unaudited Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Investments:
Fixed maturities available for sale, at fair value (amortized cost: $18,447,720 and $18,143,305; net of allowance for credit losses: $3,830 and $2,397 )	$ 18,723,035	$ 18,717,825
Short-term investments available for sale, at fair value (amortized cost: $1,269,312 and $1,924,292; net of allowance for credit losses: $0 and $0)	1,269,631	1,924,922
Collateral received under securities lending, at fair value (amortized cost: $143,886 and $301,089)	143,894	301,096
Equity securities, at fair value	1,532,906	1,444,830
Other investments (portion measured at fair value: $3,935,354 and $3,824,796)	4,435,354	4,324,796
Investments accounted for using the equity method	2,256,327	2,047,889
Total investments	28,361,147	28,761,358
Cash	941,951	906,448
Accrued investment income	101,108	103,299
Securities pledged under securities lending, at fair value (amortized cost: $142,129 and $294,493)	140,949	294,912
Investment in operating affiliates	739,783	129,291
Premiums receivable (net of allowance for credit losses: $36,111 and $37,781)	2,618,175	2,064,586
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses (net of allowance for credit losses: $10,872 and $11,636)	4,041,076	4,500,802
Contractholder receivables (net of allowance for credit losses: $5,853 and $8,638)	1,919,655	1,986,924
Ceded unearned premiums	1,406,489	1,234,075
Deferred acquisition costs	919,740	790,708
Receivable for securities sold	199,424	92,743
Goodwill and intangible assets	679,509	692,863
Other assets	2,135,261	1,724,288
Total assets	44,204,267	43,282,297
Liabilities
Reserve for losses and loss adjustment expenses	16,443,952	16,513,929
Unearned premiums	5,549,127	4,838,965
Reinsurance balances payable	919,125	683,263
Contractholder payables	1,925,508	1,995,562
Collateral held for insured obligations	222,245	215,581
Senior notes	2,861,417	2,861,113
Revolving credit agreement borrowings	155,687	155,687
Securities lending payable	143,886	301,089
Payable for securities purchased	386,453	218,779
Other liabilities	1,565,861	1,510,888
Total liabilities	30,173,261	29,294,856
Commitments and Contingencies
Redeemable noncontrolling interests	57,670	58,548
Shareholders' Equity
Non-cumulative preferred shares	780,000	780,000
Common shares ($0.0011 par, shares issued: 581,226,408 and 579,000,841)	645	643
Additional paid-in capital	2,014,741	1,977,794
Retained earnings	12,790,216	12,362,463
Accumulated other comprehensive income (loss), net of deferred income tax	205,827	488,895
Common shares held in treasury, at cost (shares: 177,913,031 and 172,280,199)	(2,694,957)	(2,503,909)
Total shareholders' equity available to Arch	13,096,472	13,105,886
Non-redeemable noncontrolling interests	876,864	823,007
Total shareholders' equity	13,973,336	13,928,893
Total liabilities, noncontrolling interests and shareholders' equity	$ 44,204,267	$ 43,282,297