Segment Information (Tables)

12 Months Ended

Dec. 31, 2014

Segment Reporting [Abstract]

Analysis of underwriting income by segment and reconciliation to net income available to common shareholders

The following tables summarize the Company’s underwriting income or loss by segment, together with a reconciliation of underwriting income to net income available to Arch common shareholders, summary information regarding net premiums written and earned by major line of business and net premiums written by location:

	Year Ended December 31, 2014
	Insurance			Reinsurance			Mortgage			Sub-Total			Other			Total
Gross premiums written (1)	$	3,008,669		$	1,527,245		$	227,356		$	4,760,394		$	288,627		$	4,840,616
Premiums ceded	(862,015		)	(261,254		)	(22,519		)	(1,142,912		)	(14,171		)	(948,678		)
Net premiums written	2,146,654			1,265,991			204,837			3,617,482			274,456			3,891,938
Change in unearned premiums	(129,284		)	13,337			(11,264		)	(127,211		)	(170,979		)	(298,190		)
Net premiums earned	2,017,370			1,279,328			193,573			3,490,271			103,477			3,593,748
Other underwriting income	2,135			3,167			4,840			10,142			—			10,142
Losses and loss adjustment expenses	(1,260,953		)	(532,450		)	(55,674		)	(1,849,077		)	(70,173		)	(1,919,250		)
Acquisition expenses, net	(316,308		)	(261,438		)	(49,400		)	(627,146		)	(30,116		)	(657,262		)
Other operating expenses	(335,157		)	(147,964		)	(66,891		)	(550,012		)	(6,268		)	(556,280		)
Underwriting income (loss)	$	107,087		$	340,643		$	26,448		474,178			(3,080		)	471,098
Net investment income										284,336			18,249			302,585
Net realized gains (losses)										133,384			(30,467		)	102,917
Net impairment losses recognized in earnings										(30,150		)	—			(30,150		)
Equity in net income of investment funds accounted for using the equity method										19,883			—			19,883
Other income (loss)										(10,252		)	—			(10,252		)
Other expenses										(47,615		)	(2,329		)	(49,944		)
Interest expense										(45,634		)	—			(45,634		)
Net foreign exchange gains (losses)										82,658			1,086			83,744
Income before income taxes										860,788			(16,541		)	844,247
Income tax expense										(22,987		)	—			(22,987		)
Net income										837,801			(16,541		)	821,260
Dividends attributable to redeemable noncontrolling interests										—			(14,728		)	(14,728		)
Amounts attributable to noncontrolling interests										—			27,823			27,823
Net income available to Arch										837,801			(3,446		)	834,355
Preferred dividends										(21,938		)	—			(21,938		)
Net income available to Arch common shareholders										$	815,863		$	(3,446	)	$	812,417
Underwriting Ratios
Loss ratio	62.5		%	41.6		%	28.8		%	53.0		%	67.8		%	53.4		%
Acquisition expense ratio	15.7		%	20.4		%	25.5		%	18.0		%	29.1		%	18.3		%
Other operating expense ratio	16.6		%	11.6		%	34.6		%	15.8		%	6.1		%	15.5		%
Combined ratio	94.8		%	73.6		%	88.9		%	86.8		%	103.0		%	87.2		%
Goodwill and intangible assets	$	28,331		$	3,333		$	77,875		$	109,539		$	—		$	109,539
Total investable assets										$	14,609,969		$	1,163,240		$	15,773,209
Total assets										20,527,027			1,482,516			22,009,543
Total liabilities										14,492,237			398,660			14,890,897

(1) Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total.

	Year Ended December 31, 2013
	Insurance			Reinsurance			Mortgage			Sub-Total			Other		Total
Gross premiums written (1)	$	2,712,509		$	1,399,621		$	89,570		$	4,196,623		$	—	$	4,196,623
Premiums ceded	(763,713		)	(86,620		)	—			(845,256		)	—		(845,256		)
Net premiums written	1,948,796			1,313,001			89,570			3,351,367			—		3,351,367
Change in unearned premiums	(72,782		)	(94,329		)	(38,304		)	(205,415		)	—		(205,415		)
Net premiums earned	1,876,014			1,218,672			51,266			3,145,952			—		3,145,952
Other underwriting income	2,122			5,258			259			7,639			—		7,639
Losses and loss adjustment expenses	(1,188,445		)	(486,236		)	(4,743		)	(1,679,424		)	—		(1,679,424		)
Acquisition expenses, net	(311,904		)	(234,373		)	(17,826		)	(564,103		)	—		(564,103		)
Other operating expenses	(315,387		)	(134,563		)	(8,377		)	(458,327		)	—		(458,327		)
Underwriting income (loss)	$	62,400		$	368,758		$	20,579		451,737			—		451,737
Net investment income										267,219			—		267,219
Net realized gains										74,018			—		74,018
Net impairment losses recognized in earnings										(3,786		)	—		(3,786		)
Equity in net income (loss) of investment funds accounted for using the equity method										35,701			—		35,701
Other income (loss)										(586		)	—		(586		)
Other expenses										(42,403		)	—		(42,403		)
Interest expense										(27,060		)	—		(27,060		)
Net foreign exchange gains (losses)										(12,335		)	—		(12,335		)
Income before income taxes										742,505			—		742,505
Income tax expense										(32,774		)	—		(32,774		)
Net income										709,731			—		709,731
Dividends attributable to redeemable noncontrolling interests										—			—		—
Amounts attributable to noncontrolling interests										—			—		—
Net income available to Arch										709,731			—		709,731
Preferred dividends										(21,938		)	—		(21,938		)
Net income available to Arch common shareholders										$	687,793		$	—	$	687,793
Underwriting Ratios
Loss ratio	63.3		%	39.9		%	9.3		%	53.4		%	—		53.4		%
Acquisition expense ratio	16.6		%	19.2		%	34.8		%	17.9		%	—		17.9		%
Other operating expense ratio	16.8		%	11.0		%	16.3		%	14.6		%	—		14.6		%
Combined ratio	96.7		%	70.1		%	60.4		%	85.9		%	—		85.9		%
Goodwill and intangible assets	$	20,419		$	6,900		$	—		$	27,319		$	—	$	27,319
Total investable assets										$	14,049,525		$	—	$	14,049,525
Total assets										19,566,094			—		19,566,094
Total liabilities										13,918,598			—		13,918,598

(1) Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total.

	Year Ended December 31, 2012
	Insurance			Reinsurance			Mortgage			Sub-Total			Other			Total
Gross premiums written (1)	$	2,593,959		$	1,213,889		$	68,111		$	3,869,161		$	—		$	3,869,161
Premiums ceded	(768,625		)	(55,099		)	—			(816,926		)	—			(816,926		)
Net premiums written	1,825,334			1,158,790			68,111			3,052,235			—			3,052,235
Change in unearned premiums	(24,991		)	(40,663		)	(51,441		)	(117,095		)	—			(117,095		)
Net premiums earned	1,800,343			1,118,127			16,670			2,935,140			—			2,935,140
Other underwriting income	2,335			5,755			—			8,090			—			8,090
Losses and loss adjustment expenses	(1,283,841		)	(574,821		)	(2,615		)	(1,861,277		)	—			(1,861,277		)
Acquisition expenses, net	(298,983		)	(204,903		)	(4,998		)	(508,884		)	—			(508,884		)
Other operating expenses	(307,489		)	(118,245		)	(4,301		)	(430,035		)	—			(430,035		)
Underwriting income (loss)	$	(87,635	)	$	225,913		$	4,756		143,034			—			143,034
Net investment income										294,895			—			294,895
Net realized gains										194,228			—			194,228
Net impairment losses recognized in earnings										(11,388		)	—			(11,388		)
Equity in net income (loss) of investment funds accounted for using the equity method										73,510			—			73,510
Other income (loss)										(12,094		)	—			(12,094		)
Other expenses										(35,318		)	—			(35,318		)
Interest expense										(28,525		)	—			(28,525		)
Net foreign exchange gains (losses)										(28,955		)	—			(28,955		)
Income before income taxes										589,387			—			589,387
Income tax benefit										4,010			—			4,010
Net income										593,397			—			593,397
Dividends attributable to redeemable noncontrolling interests										—			—			—
Amounts attributable to noncontrolling interests										—			—			—
Net income available to Arch										593,397			—			593,397
Preferred dividends										(25,079		)	—			(25,079		)
Loss on repurchase of preferred shares										(10,612		)	—			(10,612		)
Net income available to Arch common shareholders										$	557,706		$	—		$	557,706
Underwriting Ratios
Loss ratio	71.3		%	51.4		%	15.7		%	63.4		%	—		%	63.4		%
Acquisition expense ratio	16.6		%	18.3		%	30.0		%	17.3		%	—		%	17.3		%
Other operating expense ratio	17.1		%	10.6		%	25.8		%	14.7		%	—		%	14.7		%
Combined ratio	105.0		%	80.3		%	71.5		%	95.4		%	—		%	95.4		%
Goodwill and intangible assets	$	21,357		$	16,902		$	—		$	38,259		$	—		$	38,259
Total investable assets										$	13,045,134		$	—		$	13,045,134
Total assets										17,816,762			—			17,816,762
Total liabilities										12,647,884			—			12,647,884

(1) Certain amounts included in the gross premiums written of each segment are related to intersegment transactions. Accordingly, the sum of gross premiums written for each segment does not agree to the total gross premiums written as shown in the table above due to the elimination of intersegment transactions in the total.

Summary of information regarding net premiums written and earned by major line of business and net premiums written by location

The following tables provide summary information regarding net premiums written and earned by major line of business and net premiums written by location:

INSURANCE SEGMENT	Year Ended December 31,
	2014		2013		2012
Net premiums written (1)
Programs	$	480,580	$	419,673	$	340,130
Professional lines (2)	476,604		476,193		548,423
Construction and national accounts	286,994		271,110		211,130
Property, energy, marine and aviation	244,640		280,551		294,690
Excess and surplus casualty (3)	212,519		149,286		112,307
Travel, accident and health	145,732		104,903		106,871
Lenders products	100,407		101,576		99,724
Other (4)	199,178		145,504		112,059
Total	$	2,146,654	$	1,948,796	$	1,825,334
Net premiums earned (1)
Programs	$	460,392	$	386,840	$	318,740
Professional lines (2)	456,508		491,791		536,971
Construction and national accounts	277,811		250,729		209,217
Property, energy, marine and aviation	244,974		304,294		313,081
Excess and surplus casualty (3)	182,024		118,395		113,597
Travel, accident and health	127,691		97,135		98,686
Lenders products	94,438		99,847		103,478
Other (4)	173,532		126,983		106,573
Total	$	2,017,370	$	1,876,014	$	1,800,343
Net premiums written by client location (1)
United States	$	1,726,181	$	1,526,156	$	1,314,577
Europe	240,136		226,254		271,278
Asia and Pacific	79,564		95,970		120,492
Other	100,773		100,416		118,987
Total	$	2,146,654	$	1,948,796	$	1,825,334
Net premiums written by underwriting location (1)
United States	$	1,688,887	$	1,478,930	$	1,254,623
Europe	394,430		389,763		472,132
Other	63,337		80,103		98,579
Total	$	2,146,654	$	1,948,796	$	1,825,334

(1) Insurance segment results include premiums written and earned assumed through intersegment transactions and exclude premiums written and earned ceded through intersegment transactions.

(2) Includes professional liability, executive assurance and healthcare business.

(3) Includes casualty and contract binding business.

(4) Includes alternative markets, excess workers' compensation and surety business.

REINSURANCE SEGMENT	Year Ended December 31,
	2014		2013		2012
Net premiums written (1)
Other specialty (2)	$	405,126	$	417,865	$	308,104
Property excluding property catastrophe (3)	343,043		292,536		265,783
Casualty (4)	317,996		306,304		205,925
Property catastrophe	137,471		220,749		283,677
Marine and aviation	50,444		64,380		84,649
Other (5)	11,911		11,167		10,652
Total	$	1,265,991	$	1,313,001	$	1,158,790
Net premiums earned (1)
Other specialty (2)	$	424,725	$	387,630	$	309,101
Property excluding property catastrophe (3)	303,496		274,719		254,338
Casualty (4)	327,518		241,774		188,963
Property catastrophe	150,761		232,423		280,185
Marine and aviation	61,118		70,105		76,145
Other (5)	11,710		12,021		9,395
Total	$	1,279,328	$	1,218,672	$	1,118,127
Net premiums written (1)
Pro rata	$	663,135	$	692,024	$	530,763
Excess of loss	602,856		620,977		628,027
Total	$	1,265,991	$	1,313,001	$	1,158,790
Net premiums earned (1)
Pro rata	$	686,201	$	608,586	$	499,094
Excess of loss	593,127		610,086		619,033
Total	$	1,279,328	$	1,218,672	$	1,118,127
Net premiums written by client location (1)
United States	$	589,255	$	706,388	$	568,043
Europe	355,735		327,059		341,653
Asia and Pacific	142,626		94,252		97,879
Bermuda	77,620		87,047		72,864
Other	100,755		98,255		78,351
Total	$	1,265,991	$	1,313,001	$	1,158,790
Net premiums written by underwriting location (1)
United States	$	492,891	$	507,183	$	379,239
Bermuda	394,351		459,467		527,909
Europe	343,823		309,129		225,470
Other	34,926		37,222		26,172
Total	$	1,265,991	$	1,313,001	$	1,158,790

(1) Reinsurance segment results include premiums written and earned assumed through intersegment transactions and exclude premiums written and earned ceded through intersegment transactions.

(2) Includes non-excess motor, surety, accident and health, workers’ compensation catastrophe, agriculture, trade credit and other.

(3) Includes facultative business.

(4) Includes executive assurance, professional liability, workers’ compensation, excess motor, healthcare and other.

(5) Includes life, casualty clash and other.

	Year Ended December 31,
MORTGAGE SEGMENT	2014		2013		2012
Net premiums written by client location
United States	$	184,333	$	63,692	$	61,571
Other	20,504		25,878		6,540
Total	$	204,837	$	89,570	$	68,111
Net premiums written by underwriting location
United States	$	98,809	$	—	$	—
Other	106,028		89,570		68,111
Total	$	204,837	$	89,570	$	68,111

OTHER SEGMENT	Year Ended December 31,
	2014		2013		2012
Net premiums written (1)
Casualty (2)	$	179,054	$	—	$	—
Other specialty (3)	66,524		—		—
Property catastrophe	9,280		—		—
Marine and aviation	1,251		—		—
Property excluding property catastrophe	564		—		—
Other (4)	17,783		—		—
Total	$	274,456	$	—	$	—
Net premiums earned (1)
Casualty (2)	$	72,395	$	—	$	—
Other specialty (3)	24,157		—		—
Property catastrophe	5,115		—		—
Marine and aviation	789		—		—
Property excluding property catastrophe	182		—		—
Other (4)	839		—		—
Total	$	103,477	$	—	$	—
Net premiums written by client location (1)
United States	$	186,795	$	—	$	—
Europe	54,131		—		—
Bermuda	27,977		—		—
Other	5,553		—		—
Total	$	274,456	$	—	$	—

(1) Other segment results include premiums written and earned assumed through intersegment transactions and exclude premiums written and earned ceded through intersegment transactions.

(2) Includes professional liability, excess motor, programs and other.

(3) Includes non-excess motor and other.

(4) Includes mortgage and other.