Investments - Major Categories of Net Investment Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Investment Income [Line Items]
Gross investment income									$ 167,925	$ 111,750	$ 96,605
Investment expenses									(10,271)	(10,344)	(6,685)
Net investment income	$ 51,599	$ 40,286	$ 34,779	$ 30,990	$ 24,889	$ 25,706	$ 26,485	$ 24,326	157,654	101,406	89,920
Fixed maturity investments
Net Investment Income [Line Items]
Gross investment income									123,118	95,911	72,050
Short-term investments and cash and cash equivalents
Net Investment Income [Line Items]
Gross investment income									6,163	6,682	13,705
Equity securities
Net Investment Income [Line Items]
Gross investment income									5,827	5,854	4,923
Other investments
Net Investment Income [Line Items]
Gross investment income									11,712	1,335	652
Life settlements and other
Net Investment Income [Line Items]
Gross investment income									$ 21,105	$ 1,968	$ 5,275