Summary of Significant Accounting Policies - Components of Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other Comprehensive Income (Loss), Tax, Parenthetical Disclosures [Abstract]
Tax on Unrealized gain (loss) on investments before reclassification	$ (47)	$ (41)	$ 7
Tax on Reclassification adjustment for net gain (losses) realized in net income	$ 8	$ (691)	$ 12