Reinsurance - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013 Entity		Dec. 31, 2012	Dec. 31, 2011
Effects of Reinsurance [Line Items]
Reserve for uncollectible reinsurance amount	$ 11,300,000		$ 11,500,000
Reinsurance rating description	To meet our standards of acceptability, when the reinsurance is placed, a reinsurer generally must have a rating from A.M. Best Company ("A.M. Best") and/or S&P of "A" or better, or an equivalent financial strength if not rated, plus at least $500 million in policyholders' surplus.
Reinsurance recoverables	1,108,644,000	[1],[2],[3]
Ceded premiums earned	455,985,000		396,639,000	346,172,000
Ceded losses incurred	188,733,000		262,649,000	213,393,000
Percentage of reinsurance recoverable of 20 largest reinsurers	76.30%
Number of largest reinsurers	20
Percentage of funding requirement to retain	100.00%
Reinsurance recoverables for paid and unpaid losses	860,822,000
Catastrophic
Effects of Reinsurance [Line Items]
Reinsurance recoverables for paid and unpaid losses	46,500,000		88,200,000
Superstorm Sandy
Effects of Reinsurance [Line Items]
Reinsurance recoverables for paid and unpaid losses	30,700,000		54,600,000
Hurricane Gustav and Ike
Effects of Reinsurance [Line Items]
Reinsurance recoverables for paid and unpaid losses	3,300,000		15,200,000
Letter of Credit
Effects of Reinsurance [Line Items]
Percentage of collateral held	24.00%
Minimum
Effects of Reinsurance [Line Items]
Policyholders' surplus for reinsurance	$ 500,000,000
Percentage of collateral required of qualifying reinsurers	0.00%
Maximum
Effects of Reinsurance [Line Items]
Percentage of collateral required of qualifying reinsurers	100.00%

[1] Equivalent S&P rating used for certain companies when an A.M. Best rating was unavailable.

[2] Net of reserve for uncollectible reinsurance of approximately $11.3 million. The carrying value consists of reinsurance recoverables on paid losses due within 30-45 days and reinsurance on unpaid losses which by nature of our reserving process is our best estimate of the value as of December 31, 2013.

[3] Net of reserve for uncollectible reinsurance of approximately $11.3 million.