Losses and Loss Adjustment Expenses Incurred and Paid - Schedule of Frequency of Claims (Detail) $ in Thousands	Dec. 31, 2016 USD ($) Claim	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2008 USD ($)	Dec. 31, 2007 USD ($)
Claims Development [Line Items]
Incurred losses and LAE, net of reinsurance	$ 1,786,509
Accident Year 2007
Claims Development [Line Items]
Incurred losses and LAE, net of reinsurance	230,862	$ 230,877	$ 230,931	$ 231,058	$ 231,931	$ 231,729	$ 228,716	$ 228,601	$ 230,360	$ 233,004
Total of incurred but not reported liabilities plus expected development on reported claims	$ 3
Cumulative number of reported claims | Claim	117,206
Accident Year 2008
Claims Development [Line Items]
Incurred losses and LAE, net of reinsurance	$ 177,226	177,190	176,947	176,468	175,849	175,044	174,312	174,921	$ 187,583
Total of incurred but not reported liabilities plus expected development on reported claims	$ 33
Cumulative number of reported claims | Claim	100,188
Accident Year 2009
Claims Development [Line Items]
Incurred losses and LAE, net of reinsurance	$ 142,705	142,546	142,772	142,819	141,936	140,501	140,539	$ 146,584
Total of incurred but not reported liabilities plus expected development on reported claims	$ 26
Cumulative number of reported claims | Claim	78,607
Accident Year 2010
Claims Development [Line Items]
Incurred losses and LAE, net of reinsurance	$ 133,983	134,144	134,191	134,446	134,470	133,283	$ 135,458
Total of incurred but not reported liabilities plus expected development on reported claims	$ 62
Cumulative number of reported claims | Claim	71,008
Accident Year 2011
Claims Development [Line Items]
Incurred losses and LAE, net of reinsurance	$ 125,670	125,810	126,373	126,272	126,886	$ 126,384
Total of incurred but not reported liabilities plus expected development on reported claims	$ 211
Cumulative number of reported claims | Claim	65,831
Accident Year 2012
Claims Development [Line Items]
Incurred losses and LAE, net of reinsurance	$ 141,375	140,673	140,249	140,111	$ 144,231
Total of incurred but not reported liabilities plus expected development on reported claims	$ 597
Cumulative number of reported claims | Claim	73,164
Accident Year 2013
Claims Development [Line Items]
Incurred losses and LAE, net of reinsurance	$ 144,076	142,053	140,775	$ 145,878
Total of incurred but not reported liabilities plus expected development on reported claims	$ 1,784
Cumulative number of reported claims | Claim	73,714
Accident Year 2014
Claims Development [Line Items]
Incurred losses and LAE, net of reinsurance	$ 171,827	165,991	$ 166,179
Total of incurred but not reported liabilities plus expected development on reported claims	$ 6,003
Cumulative number of reported claims | Claim	84,791
Accident Year 2015
Claims Development [Line Items]
Incurred losses and LAE, net of reinsurance	$ 240,419	$ 218,186
Total of incurred but not reported liabilities plus expected development on reported claims	$ 21,968
Cumulative number of reported claims | Claim	108,755
Accident Year 2016
Claims Development [Line Items]
Incurred losses and LAE, net of reinsurance	$ 278,366
Total of incurred but not reported liabilities plus expected development on reported claims	$ 69,261
Cumulative number of reported claims | Claim	112,441