Summary of Fair Value Accumulated Other Comprehensive Income and Intraperiod Tax Allocation (Detail) - Available-for-sale Securities $ in Thousands	9 Months Ended
	Sep. 30, 2015 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Accumulated other comprehensive income, before tax	$ 15,138
Intra-period tax allocation recorded as a benefit from income taxes	(6,086)
Accumulated other comprehensive income, net of tax	$ 9,052