• Filing Date: 2018-03-07
  • Form Type: 10-K
  • Description: Annual report
v3.8.0.1
Investments (Net Investment Income) - Additional Information (Detail)
$ in Thousands
Dec. 31, 2017
USD ($)
Accounts
Bank
Dec. 31, 2016
USD ($)
Accounts
Bank
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Schedule of Investments [Line Items]        
Cash and cash equivalents $ 255,884 $ 280,531 $ 267,738 $ 314,416
Deposits representing cash and cash equivalents in percentage 34.10% 72.60%    
Number of national banks | Bank 3 3    
Number of custodial accounts | Accounts 3 3    
Federal Deposit Insurance Corporation's coverage limit for insured deposit accounts $ 250 $ 250    
Custodial Accounts [Member]        
Schedule of Investments [Line Items]        
Cash and cash equivalents 38,543 28,431    
Bank Deposits [Member]        
Schedule of Investments [Line Items]        
Cash and cash equivalents $ 87,092 $ 203,139