Disclosures about Fair Value of Assets and Liabilities - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers between levels	$ 0
Available-for-sale securities, Fair Value	48,594,000	48,084,000
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, measurement with unobservable inputs, assets, value	0		0
Available-for-sale securities, Fair Value	$ 0		$ 0