Investments - Amortized Cost and Estimated Fair Values of Company's Fixed Maturity Securities Classified as Held to Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 856,218	$ 859,387
Gross Unrealized Holding Gains	1,098	130
Gross Unrealized Holding Losses Non-OTTI	(29,925)	(59,958)
Fair Value	827,391	799,559
U.S. Government and Agency [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	19,841	19,992
Gross Unrealized Holding Gains	8	6
Gross Unrealized Holding Losses Non-OTTI	(1,227)	(1,866)
Fair Value	18,622	18,132
Non-U.S. Government [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	32,253	23,592
Gross Unrealized Holding Gains	40	19
Gross Unrealized Holding Losses Non-OTTI	(1,074)	(1,284)
Fair Value	31,219	22,327
Corporate [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	804,124	815,803
Gross Unrealized Holding Gains	1,050	105
Gross Unrealized Holding Losses Non-OTTI	(27,624)	(56,808)
Fair Value	$ 777,550	$ 759,100