Amount and Nature of Net Assets Restricted from Payment of Dividends (Parenthetical) (Detail) - Fixed maturities - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
NIC and NSIC
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Restricted net assets, amortized cost	$ 9,820	$ 9,950
NHUK
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Restricted net assets, amortized cost	$ 457,225	$ 458,558