Disclosures about Fair Value of Assets and Liabilities - Additional Information (Detail) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers between levels	$ 0	$ 0
Available-for-sale securities, Fair Value	47,820,000	47,820,000	$ 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		$ 0
Available-for-sale securities, Fair Value	$ 0	$ 0		$ 0