Changes in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (4,444)		$ (4,185)
Other comprehensive income (loss), net of tax	8,807	$ 160	8,548	$ 244
Ending balance	4,363		4,363
Net Unrealized Gains (Reclassification Adjustment) on Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), net of tax	9,052		9,052
Ending balance	9,052		9,052
Cumulative Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	333		174
Other comprehensive income (loss), net of tax	(327)		(168)
Ending balance	6		6
Defined Benefit Pension Obligation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(4,777)		(4,359)
Other comprehensive income (loss), net of tax	82		(336)
Ending balance	$ (4,695)		$ (4,695)