Investments - Amortized Cost and Estimated Fair Values of Fixed Maturity Securities Classified as Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 302,954	$ 590,588
Gross Unrealized Holding Gains	8,544	21,095
Gross Unrealized Holding Losses Non-OTTI	(856)	(4,367)
Fair Value	310,642	607,316
U.S. government and agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,532	17,816
Gross Unrealized Holding Gains	494	546
Gross Unrealized Holding Losses Non-OTTI		(433)
Fair Value	5,026	17,929
Non-U.S. government [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	122,844	160,128
Gross Unrealized Holding Gains	4,290	9,227
Gross Unrealized Holding Losses Non-OTTI	(222)	(828)
Fair Value	126,912	168,527
Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	169,117	366,954
Gross Unrealized Holding Gains	3,436	7,937
Gross Unrealized Holding Losses Non-OTTI	(538)	(2,578)
Fair Value	172,015	372,313
Residential mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,701	13,544
Gross Unrealized Holding Gains	270	276
Gross Unrealized Holding Losses Non-OTTI	(80)	(108)
Fair Value	4,891	13,712
Commercial mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,376	12,680
Gross Unrealized Holding Gains	45	3,044
Gross Unrealized Holding Losses Non-OTTI		(7)
Fair Value	1,421	15,717
Asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	384	19,466
Gross Unrealized Holding Gains	9	65
Gross Unrealized Holding Losses Non-OTTI	(16)	(413)
Fair Value	$ 377	$ 19,118

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

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

+ References+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details