Composition of Investments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Unrealized Losses	$ (9,227)
US Government Agencies Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	2,033,500	2,474,029
Available For Sale Securities Unrealized Gains	11,321	12,420
Available For Sale Securities Unrealized Losses	(1,005)	(1,488)
Available For Sale Securities Fair Value	2,043,816	2,484,961
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	6,212,908	6,228,479
Available For Sale Securities Unrealized Gains	69,901	42,149
Available For Sale Securities Unrealized Losses	(8,602)	(23,536)
Available For Sale Securities Fair Value	6,274,207	6,247,092
Public Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	47,786	58,199
Available For Sale Securities Unrealized Gains	97,815	6,802
Available For Sale Securities Unrealized Losses	(625)
Available For Sale Securities Fair Value	144,976	65,001
Debt and Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	6,260,694	6,286,678
Available For Sale Securities Unrealized Gains	167,716	48,951
Available For Sale Securities Unrealized Losses	(9,227)	(23,536)
Available For Sale Securities Fair Value	6,419,183	6,312,093
US Corporate Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	1,360,511	1,400,373
Available For Sale Securities Unrealized Gains	12,772	9,953
Available For Sale Securities Unrealized Losses	(97)	(2,573)
Available For Sale Securities Fair Value	1,373,186	1,407,753
High Yield Corporate Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	468,285	442,723
Available For Sale Securities Unrealized Gains	31,408	12,498
Available For Sale Securities Unrealized Losses	(1,076)	(7,742)
Available For Sale Securities Fair Value	498,617	447,479
Asset-backed Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	3,227	29,101
Available For Sale Securities Unrealized Gains	8	72
Available For Sale Securities Unrealized Losses	0	(25)
Available For Sale Securities Fair Value	3,235	29,148
Municipal Obligations
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	1,023,504	814,657
Available For Sale Securities Unrealized Gains	4,379	2,021
Available For Sale Securities Unrealized Losses	(366)	(597)
Available For Sale Securities Fair Value	1,027,517	816,081
Auction Rate Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	80,706	82,900
Available For Sale Securities Unrealized Losses	(5,860)	(8,304)
Available For Sale Securities Fair Value	74,846	74,596
Foreign Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	1,243,175	984,696
Available For Sale Securities Unrealized Gains	10,013	5,185
Available For Sale Securities Unrealized Losses	(198)	(2,807)
Available For Sale Securities Fair Value	$ 1,252,990	$ 987,074

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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+ Details

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References+ Details