Investments - Additional Information (Detail)	Dec. 31, 2016 USD ($) Security	Dec. 31, 2015 USD ($)
Schedule Of Investments [Line Items]
Fair value of investments, assets managed on behalf of the trade capital providers	$ 131,900,000	$ 95,300,000
Number of securities in an unrealized loss position, total | Security	7,401
Number of securities in an unrealized loss position for less than one year | Security	2,194
Number of securities in an unrealized loss position for a period of one year or greater | Security	182
Transfers between Level 1 and Level 2 securities	$ 0	0
Transfers between Level 2 and Level 1 securities	0	$ 0
Fixed Maturities Term Loan [Member]
Schedule Of Investments [Line Items]
Own term loan fixed maturity level 3 value	$ 2,000,000