Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Comprehensive Income
Net income	$ 821,260		$ 709,731		$ 593,397
Unrealized appreciation (decline) in value of available-for-sale investments:
Unrealized holding gains (losses) arising during period	146,330		(176,403)		273,931
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	(320)		(175)		(787)
Reclassification of net realized gains, net of income taxes, included in net income	(65,104)		(32,686)		(157,824)
Foreign currency translation adjustments	(27,014)		(2,789)		17,774
Comprehensive income	875,152		497,678		726,491
Amounts attributable to noncontrolling interests	13,095	[1]	0	[1]	0	[1]
Comprehensive income available to Arch	$ 888,247		$ 497,678		$ 726,491

[1] See Note 4.