Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Unrealized gains (loss) on securities, tax expense	$ (338,000)	$ (4,605,000)	$ 1,739,000
Income tax benefit (expense) attributable to stock plans	51,000	(31,000)	(608,000)
Retained earnings not provided for provision for income tax	10,750,000
Unrecognized deferred tax liability	4,391,000
Unrecognized tax benefits	$ 0	$ 0	$ 0