Unaudited Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Investments:
Fixed maturities available for sale, at fair value (amortized cost: $9,722,364 and $9,564,634)	$ 9,775,730		$ 9,571,776
Short-term investments available for sale, at fair value (amortized cost: $1,485,378 and $1,477,584)	1,484,280		1,478,367
Investment of funds received under securities lending, at fair value (amortized cost: $93,274 and $97,943)	96,264		100,584
Equity securities available for sale, at fair value (cost: $475,868 and $433,275)	548,168		496,824
Other investments available for sale, at fair value (cost: $417,762 and $488,687)	426,917		498,310
Investments accounted for using the fair value option	1,256,650		1,221,534
Investments accounted for using the equity method	255,488		244,339
Total investments	13,843,497		13,611,734
Cash	1,569,605		434,057		371,041
Accrued investment income	59,701		66,848
Investment in joint venture (cost: $100,000)	102,803		104,856
Fixed maturities and short-term investments pledged under securities lending, at fair value	100,590		105,081
Premiums receivable	1,008,375		753,924
Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses	1,790,025		1,804,330
Contractholder receivables	1,118,991		1,064,246
Prepaid reinsurance premiums	349,077		328,343
Deferred acquisition costs, net	384,294		342,314
Receivable for securities sold	426,431		50,555
Goodwill and intangible assets	120,875		27,319
Other assets	926,094		872,487
Total assets	21,800,358		19,566,094
Liabilities
Reserve for losses and loss adjustment expenses	8,938,958		8,824,696
Unearned premiums	2,148,475		1,896,365
Reinsurance balances payable	201,794		196,167
Contractholder payables	1,118,991		1,064,246
Deposit accounting liabilities	409,080		421,297
Senior notes	800,000		800,000
Revolving credit agreement borrowings	100,000		100,000
Securities lending payable	103,330		107,999
Payable for securities purchased	499,473		51,318
Other liabilities	575,394		456,510
Total liabilities	14,895,495		13,918,598
Commitments and Contingencies
Redeemable noncontrolling interests	219,234	[1]	0	[1]
Shareholders’ Equity
Non-cumulative preferred shares	325,000		325,000
Common shares ($0.0033 par, shares issued: 170,006,958 and 169,560,591)	567		565
Additional paid-in capital	320,503		299,517
Retained earnings	6,219,170		6,042,154
Accumulated other comprehensive income, net of deferred income tax	123,719		74,964
Common shares held in treasury, at cost (shares: 35,922,820 and 35,885,707)	(1,096,826)		(1,094,704)
Total shareholders' equity available to Arch	5,892,133		5,647,496
Non-redeemable noncontrolling interests	793,496	[1]	0	[1]
Total shareholders' equity	6,685,629		5,647,496
Total liabilities, noncontrolling interests and shareholders' equity	$ 21,800,358		$ 19,566,094

[1] See Note 4.