Investments - A Summary of the Company's Realized Gains and Losses on Sales, Calls or Redemptions of Investments (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]
Proceeds from sales									$ 10,990	$ 33,140	$ 36,329
Gross realized investment gains									1,354	2,741	2,436
Gross realized investment (losses)									(471)		(99)
Net realized investment gains (losses)									883	2,741	2,337
Impairments									(2,229)		(169)
Other, including gains on calls and redemptions									135	238	60
Net realized investment gains (losses)	710	(654)	(1,291)	24	66	985	137	1,791	(1,211)	2,979	2,228
Fixed Maturity Securities Available for Sale [Member]
Investment [Line Items]
Proceeds from sales									2,090	22,363	21,560
Gross realized investment gains									90	1,555	815
Net realized investment gains (losses)									90	1,555	815
Other, including gains on calls and redemptions									38	15
Net realized investment gains (losses)									128	1,570	815
Equity securities [Member]
Investment [Line Items]
Proceeds from sales									8,900	10,777	14,769
Gross realized investment gains									1,264	1,186	1,621
Gross realized investment (losses)									(471)		(98)
Net realized investment gains (losses)									793	1,186	1,523
Impairments									(2,229)
Net realized investment gains (losses)									(1,436)	1,186	1,523
Other [Member]
Investment [Line Items]
Proceeds from sales
Gross realized investment gains
Gross realized investment (losses)											(1)
Net realized investment gains (losses)											(1)
Impairments											(169)
Other, including gains on calls and redemptions									97	223	60
Net realized investment gains (losses)									$ 97	$ 223	$ (110)