Derivatives and Hedging Activities - Credit Derivatives Sold and Held (Detail) - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Credit Derivatives [Line Items]
Notional Amount	$ 9,000,000	$ 11,000,000	$ 11,000,000
Single Name Credit Default Swaps [Member]
Credit Derivatives [Line Items]
Notional Amount		$ 5,000,000	$ 5,000,000
Average Term (Years)		11 months 19 days	8 months 19 days
Payment / Performance Risk		0.87%	0.87%
Other [Member]
Credit Derivatives [Line Items]
Notional Amount	$ 9,000,000	$ 6,000,000	$ 6,000,000
Average Term (Years)	2 years 11 months 12 days	2 years 11 months 1 day	2 years 10 months 21 days
Payment / Performance Risk	7.45%	5.59%	9.58%