Fair Value Measurement - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2014	Dec. 31, 2013	Mar. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers between any levels	$ 0		$ 0
Carrying value of loans fully charged-off		0
Securities held to maturity	443,509,000	443,509,000	240,504,000	0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity	$ 0	$ 0	$ 0