Carrying Values and Estimated Fair Values of Consolidated Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Liabilities
Senior Notes	$ 1,807,252		$ 1,811,483
Carrying Value
Assets
Investments (excluding equity method investments)	18,015,400	[1]	17,831,800	[1]
Liabilities
Senior Notes	1,807,300	[2]	1,811,500	[2]
Fair Value
Assets
Investments (excluding equity method investments)	18,015,400	[1]	17,831,800	[1]
Liabilities
Senior Notes	$ 1,984,200	[2]	$ 1,946,700	[2]

[1] This table includes available-for-sale ("AFS") investments (debt and equity securities as well as partnership investments carried at fair value that are included in other invested assets). This table excludes investments accounted for using the equity method and certain loans receivable that are carried at cost, all of which are included in other invested assets. The fair value of short-term investments approximates amortized cost. The fair value of all other categories of investments is presented below.

[2] See Note 8 to the Notes to the Consolidated Financial Statements set forth in Part II, Item 8 of the 2012 10-K for additional information.