Changes in Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 4,078	$ 23,384
Other comprehensive income (loss) before reclassification	10,113	(17,321)
Amounts reclassified from accumulated other comprehensive income (loss)	(14,809)	(1,985)
Other comprehensive income (loss), net of tax	(4,696)	(19,306)	$ (30,644)
Ending balance	(618)	4,078	23,384
Unrealized Gains and Losses on Available for Sale Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	4,200	23,647
Other comprehensive income (loss) before reclassification	10,374	(17,065)
Amounts reclassified from accumulated other comprehensive income (loss)	(15,128)	(2,382)
Other comprehensive income (loss), net of tax	(4,754)	(19,447)
Ending balance	(554)	4,200	23,647
Foreign Currency Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(122)	(263)
Other comprehensive income (loss) before reclassification	(261)	(256)
Amounts reclassified from accumulated other comprehensive income (loss)	319	397
Other comprehensive income (loss), net of tax	58	141
Ending balance	$ (64)	$ (122)	$ (263)