Loss and Loss Adjustment Expenses - Reconciliation of Beginning and Ending Reserve Balances, Net of Related Amounts Recoverable from Reinsurers (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Liability for Unpaid Claims and Claims Adjustment Expense, Activity in Liability [Abstract]
Balance, beginning of period	$ 687,602	$ 614,557	$ 570,450
Less amounts recoverable from reinsurers on unpaid loss and loss adjustment expenses	59,334	48,699	55,190
Net balance, beginning of period	628,268	565,858	515,260
Add incurred related to:
Current accident year	262,387	268,633	241,584
Prior accident years	(47,814)	(23,717)	(12,611)
Total incurred	214,573	244,916	228,973
Less paid related to:
Current accident year	53,955	52,848	51,169
Prior accident years	135,711	129,658	127,206
Total paid	189,666	182,506	178,375
Net balance, end of period	653,175	628,268	565,858
Net balance, end of period	653,175	628,268	565,858
Add amounts recoverable from reinsurers on unpaid loss and loss adjustment expenses	64,858	59,334	48,699
Balance, end of period	$ 718,033	$ 687,602	$ 614,557