XML 63 R47.htm IDEA: XBRL DOCUMENT v3.3.1.900
Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Schedule Of Accounting Policies [Line Items]      
Percentage of comparable consolidated amounts 95.00% 95.00% 95.00%
Original maturity of cash equivalent 90 days    
Experience rated commission and other operating costs $ 300,000 $ 0 $ (9,300,000)
Advertising expense 700,000 500,000 $ 500,000
Premium tax benefit $ 3,800,000 $ 4,000,000  
Assessment Related premium Payment period 1 year    
Assessment Related loss Payment period 1 year    
Land and Office Building [Member]      
Schedule Of Accounting Policies [Line Items]      
Estimated useful life of assets 39 years    
Limited Partnership [Member]      
Schedule Of Accounting Policies [Line Items]      
Unfunded commitments $ 0    
Maximum [Member]      
Schedule Of Accounting Policies [Line Items]      
Short-term investments maturity period P1Y    
Maximum [Member] | Other Fixed Assets [Member]      
Schedule Of Accounting Policies [Line Items]      
Estimated useful life of assets 7 years    
Minimum [Member]      
Schedule Of Accounting Policies [Line Items]      
Short-term investments maturity period P3M    
Minimum [Member] | Other Fixed Assets [Member]      
Schedule Of Accounting Policies [Line Items]      
Estimated useful life of assets 3 years