Amounts Recorded for Margin Borrowing Facilities and 7.75% Subordinated Notes (Detail) - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Net Carrying Amount		$ 172,034	$ 174,673
7.75% Subordinated Notes due 2045
Debt Instrument [Line Items]
Outstanding Principal		100,000
Unamortized Debt Issuance Costs		(3,612)
Net Carrying Amount	[1]	$ 96,388

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