Investment - Major Categories of the Company's Net Investment Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Investment [Line Items]
Total gross investment income									$ 28,402	$ 28,102	$ 27,540
Investment expenses									(1,373)	(1,084)	(1,200)
Net investment income	6,763	6,947	6,649	6,670	6,698	6,801	6,605	6,914	27,029	27,018	26,340
Other Investments [Member]
Investment [Line Items]
Total gross investment income									803
Equity securities [Member]
Investment [Line Items]
Total gross investment income									543	446	181
Fixed Maturity Securities Available for Sale [Member]
Investment [Line Items]
Total gross investment income									26,422	27,167	26,769
Short-term Investments [Member]
Investment [Line Items]
Total gross investment income									$ 634	$ 489	$ 590