Outstanding Debt (Detail) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Debt		$ 287,324	$ 294,713
7.75% Subordinated Notes due 2045
Debt Instrument [Line Items]
Debt	[1]	96,680	96,619
7.875% Subordinated Notes due 2047
Debt Instrument [Line Items]
Debt	[2]	125,935	125,864
Margin borrowing facilities
Debt Instrument [Line Items]
Debt		$ 64,709	$ 72,230

[1] As of June 30, 2018 and December 31, 2017, the carrying value and fair value of the 7.75% Subordinated Notes due 2045 are net of unamortized debt issuance cost of $3.3 million.

[2] As of June 30, 2018 and December 31, 2017, the carrying value and fair value of the 7.875% Subordinated Notes due 2047 are net of unamortized debt issuance cost of $4.1 million.