Investments - Credit Ratings Company's Fixed Maturity Investments Held to Maturity (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 856,218	$ 859,387
Fair Value	827,391	799,559
% of Total Fair Value	100.00%	100.00%
AAA [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	66,044	47,949
Fair Value	63,038	44,552
% of Total Fair Value	7.60%	5.60%
AA [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	191,778	259,163
Fair Value	183,635	239,188
% of Total Fair Value	22.20%	29.90%
A [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	502,994	496,986
Fair Value	486,935	463,001
% of Total Fair Value	58.80%	57.90%
BBB or Lower [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	94,975	54,759
Fair Value	93,355	52,282
% of Total Fair Value	11.30%	6.50%
Not Rated [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	427	530
Fair Value	$ 428	$ 536
% of Total Fair Value	0.10%	0.10%