Investments - Reconciliation of Beginning and Ending Balances for All Investments Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Level 3 investments, beginning of period	$ 270,903	$ 206,671
Purchases	23,292	8,991
Sales	(2,983)	(9,284)
Total realized and unrealized gains through earnings	10,796	12,864
Net transfers into and/or (out of) Level 3
Level 3 investments, end of period	302,008	219,242
Fixed Maturity Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Level 3 investments, beginning of period	609	540
Purchases
Sales
Total realized and unrealized gains through earnings	(2)	15
Net transfers into and/or (out of) Level 3
Level 3 investments, end of period	607	555
Other Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Level 3 investments, beginning of period	265,569	202,730
Purchases	23,292	8,991
Sales	(2,983)	(9,284)
Total realized and unrealized gains through earnings	10,773	12,250
Net transfers into and/or (out of) Level 3
Level 3 investments, end of period	296,651	214,687
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Level 3 investments, beginning of period	4,725	3,401
Purchases
Sales
Total realized and unrealized gains through earnings	25	599
Net transfers into and/or (out of) Level 3
Level 3 investments, end of period	$ 4,750	$ 4,000