Securities - Available for Sale Securities (Unrealized Loss Position) (Parenthetical) (Detail) - Maximum [Member] - Other Securities [Member] - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses, available for sale securities	$ 1,000,000	$ 1,000,000	$ 1,000,000
Gross unrealized losses, held-to-maturity securities	$ 1,000,000