Investments - Transfers in and Out of Each of Valuation Levels of Fair Values (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Inputs, Level 1 [Member]
Transfers In And Out Of Each Of The Valuation Levels Of Fair Values Of Investments[Line Items]
Transfers In	$ 19,416	$ 48,536	$ 0
Transfers Out	0	0	0
Transfers Net	19,416	48,536	0
Fair Value, Inputs, Level 2 [Member]
Transfers In And Out Of Each Of The Valuation Levels Of Fair Values Of Investments[Line Items]
Transfers In	50,805	0	51,886
Transfers Out	(19,416)	(92,330)	0
Transfers Net	31,389	(92,330)	51,886
Fair Value, Inputs, Level 3 [Member]
Transfers In And Out Of Each Of The Valuation Levels Of Fair Values Of Investments[Line Items]
Transfers In	0	43,794	0
Transfers Out	(50,805)	0	(51,886)
Transfers Net	$ (50,805)	$ 43,794	$ (51,886)