Amounts Recorded for Margin Borrowing Facilities and 7.75% Subordinated Notes (Detail) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Net Carrying Amount		$ 163,143	$ 172,034
7.75% Subordinated Notes due 2045
Debt Instrument [Line Items]
Outstanding Principal		100,000	100,000
Unamortized Debt Issuance Costs		(3,503)	(3,612)
Net Carrying Amount	[1]	$ 96,497	$ 96,388

[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.