Results of Transatlantic Since Acquisition Date Included in Consolidated Statements of Earnings and Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended						0 Months Ended	10 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011		Mar. 06, 2012 TransRe	Dec. 31, 2012 TransRe
Revenues
Net premiums earned									$ 4,239,216		$ 3,733,005		$ 747,639			$ 2,915,900
Net investment income									465,664		312,998		108,910			222,000
Net realized capital gains									232,119		157,879		127,141			10,300
Other than temporary impairment losses									(44,047)		(2,907)		(3,607)
Gain on bargain purchase											494,940				494,940
Other income									78,702		57,297		1,754			25,500
Total revenues	1,362,500	1,189,500	1,196,200	1,223,600	1,240,400	1,229,500	1,234,400	1,048,900	4,971,654		4,753,212		981,837			3,173,700
Costs and Expenses
Net loss and loss adjustment expenses									2,479,353		2,630,170		429,986			2,058,100
Commissions, brokerage and other underwriting expenses									1,339,191	[1]	882,502	[1]	268,125	[1]		591,100
Other operating expenses									164,859		123,700		31,101			67,900
Corporate administration									36,111		75,842		41,007
Amortization of intangible assets									10,164		253,298		3,355			249,900
Interest expense									86,740		68,424		17,426			40,500
Total costs and expenses									4,116,418		4,033,936		791,000			3,007,500
Earnings before income taxes									855,236		719,276		190,837			166,200
Income taxes									225,882		17,032		47,586			2,400
Net earnings									$ 629,354		$ 702,244		$ 143,251			$ 163,800

[1] Includes amortization associated with deferred acquisition costs of $973.5 million, $578.1 million and $141.4 million for the years ended December 31, 2013, 2012 and 2011, respectively.