Maximum Potential Amount of Future Payments, Credit Rating and Maturity Dates for Credit Default Swaps (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Credit Derivatives [Line Items]
Maximum Potential Amount of Future Payments	$ 210,000	$ 210,000
Corporate securities
Credit Derivatives [Line Items]
Maximum Potential Amount of Future Payments	$ 120,000	120,000
Corporate securities | Credit Rating
Credit Derivatives [Line Items]
Credit Rating	A
Sovereign Debt Securities
Credit Derivatives [Line Items]
Maximum Potential Amount of Future Payments	$ 90,000	$ 90,000
Sovereign Debt Securities | Credit Rating
Credit Derivatives [Line Items]
Credit Rating	AA-A
Minimum | Corporate securities
Credit Derivatives [Line Items]
Maturity Date Range	2017-06	2017-06
Minimum | Sovereign Debt Securities
Credit Derivatives [Line Items]
Maturity Date Range	2017-06	2017-06
Maximum | Corporate securities
Credit Derivatives [Line Items]
Maturity Date Range	2020-12	2020-12
Maximum | Sovereign Debt Securities
Credit Derivatives [Line Items]
Maturity Date Range	2020-03	2020-03