Investments - Investment Income (Expense) Comprised Primarily of Interest and Dividends (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]
Total investment income									$ 7,440	$ 4,446	$ 3,550
Less: Investment expenses									(2,285)	(2,071)	(1,622)
Net investment (expense) income	$ 1,779	$ 1,307	$ 1,207	$ 862	$ 801	$ 644	$ 412	$ 518	5,155	2,375	1,928
Fixed Maturities [Member]
Net Investment Income [Line Items]
Investment income									5,642	3,329	1,420
Equity Securities [Member]
Net Investment Income [Line Items]
Investment income									1,143	988	1,982
Short-term Investments [Member]
Net Investment Income [Line Items]
Investment income									246	46
Other [Member]
Net Investment Income [Line Items]
Investment income									$ 409	$ 83	$ 148