Accumulated Other Comprehensive Income - Changes, net of tax, in Accumulated Other Comprehensive income (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	$ 6,516
Other comprehensive income (loss) before reclassifications	(20,023)
Reclassifications from accumulated other comprehensive income	(5,223)
Other Comprehensive Income (Loss), Net of Tax	(25,246)	5,570	203
Balance, end of period	(18,730)	6,516
Unrealized Gain (Loss) on Securities
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	6,921
Other comprehensive income (loss) before reclassifications	(20,043)
Reclassifications from accumulated other comprehensive income	(5,223)
Other Comprehensive Income (Loss), Net of Tax	(25,266)
Balance, end of period	(18,345)
Cumulative Translation Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(405)
Other comprehensive income (loss) before reclassifications	20
Reclassifications from accumulated other comprehensive income	0
Other Comprehensive Income (Loss), Net of Tax	20
Balance, end of period	$ (385)