Derivatives and Hedging Activities - Summary of Cash Flow Hedges (Parenthetical) (Detail) - Cash flow hedge instruments [Member] - USD ($)	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Net gain on accumulated other comprehensive income (loss)	$ 8,861,000	$ 8,404,000
Unrealized gain (loss) on cash flow hedges [Member]
Derivatives, Fair Value [Line Items]
Net gain on accumulated other comprehensive income (loss)	$ 8,237,000	$ 8,480,000
Maturity period of cash flow hedges derivatives	12 months
Maturities In Next Twelve Months [Member] | Unrealized gain (loss) on cash flow hedges [Member]
Derivatives, Fair Value [Line Items]
Net gain on accumulated other comprehensive income (loss)	$ 8,112