Investments - Summary of Net Investment Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Investments Schedule [Abstract]
Fixed income securities	$ 86,331	$ 112,652
Short-term investments	595	313
Loans	108	216
Investment expense	(1,422)	(1,064)
Securities available-for-sale and short-term	85,612	112,117
Other investments	(543)
Total net investment income	$ 85,069	$ 112,117