Changes in Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 20,102	$ 34,001	$ 23,384	$ 54,028	$ 54,028
Other comprehensive income (loss) before reclassification	(9,056)	(7,523)	(9,622)	6,238
Amounts reclassified from accumulated other comprehensive income (loss)	2,199	(1,524)	(517)	(35,312)
Other comprehensive income (loss), net of taxes	(6,857)	(9,047)	(10,139)	(29,074)
Ending balance	13,245	24,954	13,245	24,954	23,384
Unrealized Gains and Losses on Available for Sale Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	20,201	33,928	23,647	53,950	53,950
Other comprehensive income (loss) before reclassification	(9,009)	(7,295)	(9,413)	6,396
Amounts reclassified from accumulated other comprehensive income (loss)	2,129	(1,523)	(913)	(35,236)
Other comprehensive income (loss), net of taxes	(6,880)	(8,818)	(10,326)	(28,840)
Ending balance	13,321	25,110	13,321	25,110	23,647
Foreign Currency Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(99)	73	(263)	78	78
Other comprehensive income (loss) before reclassification	(47)	(228)	(209)	(158)
Amounts reclassified from accumulated other comprehensive income (loss)	70	(1)	396	(76)
Other comprehensive income (loss), net of taxes	23	(229)	187	(234)
Ending balance	$ (76)	$ (156)	$ (76)	$ (156)	$ (263)