Current Fair Value of Debt (Detail) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt		$ 163,143	$ 172,034
Debt, fair value		162,343	167,394
7.75% Subordinated Notes due 2045
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt	[1]	96,497	96,388
Debt, fair value	[1]	95,697	91,748
Margin borrowing facilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt		66,646	75,646
Debt, fair value		$ 66,646	$ 75,646

[1] As of December 31, 2016 and 2015, the carrying value and fair value of the 7.75% Subordinated Notes due 2045 are net of unamortized debt issuance cost of $3.5 million and $3.6 million, respectively.