Investments - Net Investment Income (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Net Investment Income [Line Items]
Gross investment income	$ 57,449	$ 37,415	$ 118,792	$ 69,427
Investment expenses	(3,226)	(2,760)	(4,506)	(4,355)
Net investment income	54,223	34,655	114,286	65,072
Fixed maturity investments
Net Investment Income [Line Items]
Gross investment income	40,531	28,551	77,109	54,800
Short-term investments and cash and cash equivalents
Net Investment Income [Line Items]
Gross investment income	870	1,387	2,049	4,106
Equity securities
Net Investment Income [Line Items]
Gross investment income	1,387	1,315	2,509	2,996
Other investments
Net Investment Income [Line Items]
Gross investment income	5,693	3,558	11,727	4,440
Funds held
Net Investment Income [Line Items]
Gross investment income	7,633	(184)	15,237	(10)
Life settlements and other
Net Investment Income [Line Items]
Gross investment income	$ 1,335	$ 2,788	$ 10,161	$ 3,095