Components of Net Realized Investment Gains (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
Schedule of Available-for-sale Securities [Line Items]
Total net realized investment gains	$ 17,208	$ 1,641	$ 2,806	$ 5,757	$ (158)	$ 3,211	$ 1,941	$ 1,761	$ 27,412	$ 6,755	$ 21,473
Not Designated as Hedging Instrument | Interest Rate Swap
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains									1,668
Gross realized losses									(241)
Total net realized investment gains									1,427
Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains									1,857	4,100	15,295
Gross realized losses									(691)	(1,800)	(3,511)
Total net realized investment gains									1,166	2,300	11,784
Common Shares
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains									27,302	10,630	15,792
Gross realized losses									(2,483)	(6,175)	(6,862)
Total net realized investment gains									24,819	4,455	8,930
Preferred Stock
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains											1,546
Total net realized investment gains											1,546
Other Invested Assets
Schedule of Available-for-sale Securities [Line Items]
Gross realized losses											(787)
Total net realized investment gains											$ (787)