Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Unrealized gains (loss) on securities, tax expense	$ 600,000	$ (338,000)	$ (4,600,000)
Income tax benefit (expense) attributable to stock plans	32,000	51,000	(31,000)
Retained earnings not provided for provision for income tax	10,800,000
Unrecognized deferred tax liability	4,400,000
Unrecognized tax benefits	$ 0	$ 0	$ 0