Investments - Summary of Investments Classified as Available-for-Sale in Unrealized Loss Position as Well as Aggregate Fair Value and Gross Unrealized Loss by Length of Time (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Fair Value, 12 Months or Greater
Unrealized Losses, 12 Months or Greater
Fair Value, Less Than 12 Months	89,533	121,830
Unrealized Losses, Less Than 12 Months	(796)	(439)
Fair Value, Total	89,533	121,830
Unrealized Losses, Total	(796)	(439)
U.S. Government and Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, 12 Months or Greater
Unrealized Losses, 12 Months or Greater
Fair Value, Less Than 12 Months	7,234	11,416
Unrealized Losses, Less Than 12 Months	(32)	(10)
Fair Value, Total	7,234	11,416
Unrealized Losses, Total	(32)	(10)
Non-U.S. Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, 12 Months or Greater
Unrealized Losses, 12 Months or Greater
Fair Value, Less Than 12 Months	21,758	20,406
Unrealized Losses, Less Than 12 Months	(616)	(22)
Fair Value, Total	21,758	20,406
Unrealized Losses, Total	(616)	(22)
Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, 12 Months or Greater
Unrealized Losses, 12 Months or Greater
Fair Value, Less Than 12 Months	35,416	51,478
Unrealized Losses, Less Than 12 Months	(115)	(259)
Fair Value, Total	35,416	51,478
Unrealized Losses, Total	(115)	(259)
Residential Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, 12 Months or Greater
Unrealized Losses, 12 Months or Greater
Fair Value, Less Than 12 Months	1,516	13,632
Unrealized Losses, Less Than 12 Months	(3)	(118)
Fair Value, Total	1,516	13,632
Unrealized Losses, Total	(3)	(118)
Asset-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, 12 Months or Greater
Unrealized Losses, 12 Months or Greater
Fair Value, Less Than 12 Months	23,609	24,898
Unrealized Losses, Less Than 12 Months	(30)	(30)
Fair Value, Total	23,609	24,898
Unrealized Losses, Total	$ (30)	$ (30)