Amount and Nature of Net Assets Restricted from Payment of Dividends (Parenthetical) (Detail) - Fixed maturities - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
NIC and NSIC
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Restricted net assets, amortized cost	$ 9,950	$ 10,086
NHUK
Restricted Assets And Liabilities Relating To Securitization [Line Items]
Restricted net assets, amortized cost	$ 458,558	$ 445,504