Investments - Effect of Trading Activities by Type of Instrument and by Line Item in Condensed Consolidated Statements of Income (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net Investment Income [Line Items]
Total realized gains (losses) on trading portfolio	$ (16,037)	$ (11,943)	$ 2,350
Total change in unrealized gains (losses) on trading portfolio	7,874	9,443	(18,410)
Net gains (losses) recognized on trading portfolio	(8,163)	(2,500)	(16,060)
Fixed Maturities [Member]
Net Investment Income [Line Items]
Total realized gains (losses) on trading portfolio			(3,206)
Total change in unrealized gains (losses) on trading portfolio	13	195	8,472
Equity Securities [Member]
Net Investment Income [Line Items]
Total realized gains (losses) on trading portfolio	(15,969)	(12,286)	5,816
Total change in unrealized gains (losses) on trading portfolio	7,758	9,158	(26,762)
Derivatives (Non-Hedging Instruments) [Member]
Net Investment Income [Line Items]
Total realized gains (losses) on trading portfolio	(68)	343	(260)
Total change in unrealized gains (losses) on trading portfolio	89	145	25
Other Investments [Member]
Net Investment Income [Line Items]
Total change in unrealized gains (losses) on trading portfolio	$ 14	$ (55)	$ (145)

Investments - Effect of Trading Activities by Type of Instrument and by Line Item in Condensed Consolidated Statements of Income (Detail) (USD $)
In Thousands, unless otherwise specified

12 Months Ended

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Net Investment Income [Line Items]

Total realized gains (losses) on trading portfolio

$ (16,037)

$ (11,943)

$ 2,350

Total change in unrealized gains (losses) on trading portfolio

7,874

9,443