Accumulated Other Comprehensive Income - Activity in Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Accumulated Net Unrealized Investment Gain (Loss) [Member]	Sep. 30, 2013 Accumulated Net Unrealized Investment Gain (Loss) [Member]	Sep. 30, 2014 Accumulated Net Unrealized Investment Gain (Loss) [Member]	Sep. 30, 2013 Accumulated Net Unrealized Investment Gain (Loss) [Member]	Sep. 30, 2014 Accumulated Net Unrealized Investment Gain (Loss) [Member] Interest-Only Strip [Member]	Sep. 30, 2014 Accumulated Net Unrealized Investment Gain (Loss) [Member] Interest-Only Strip [Member]	Sep. 30, 2013 Accumulated Net Unrealized Investment Gain (Loss) [Member] Interest-Only Strip [Member]	Jun. 30, 2013 Accumulated Net Unrealized Investment Gain (Loss) [Member] Interest-Only Strip [Member]	Sep. 30, 2014 Tax (Expense) Benefit [Member]	Sep. 30, 2013 Tax (Expense) Benefit [Member]	Sep. 30, 2014 Tax (Expense) Benefit [Member]	Sep. 30, 2013 Tax (Expense) Benefit [Member]
Accumulated Other Comprehensive Income [Line Items]
Balance at beginning of period	$ (2,150)	$ 1,634	$ (9,380)	$ 5,418	$ (5,534)	$ 915	$ (18,187)	$ 7,348	$ 17	$ 16	$ 16	$ 17	$ 3,367	$ 702	$ 8,791	$ (1,946)
Other comprehensive (loss) income before reclassification	(2,848)	(5,492)	6,167	(8,964)	(4,947)	(10,020)	9,491	(16,141)	(3)	(2)	1		2,102	4,528	(3,322)	7,176
Reclassification from accumulated other comprehensive income	(67)	(611)	(1,852)	(923)	(67)	(611)	(1,852)	(923)
Other comprehensive (loss) income	(2,915)	(6,103)	4,315	(9,887)	(5,014)	(10,631)	7,639	(17,064)	(3)	(2)	1		2,102	4,528	(3,322)	7,176
Balance at end of period	$ (5,065)	$ (4,469)	$ (5,065)	$ (4,469)	$ (10,548)	$ (9,716)	$ (10,548)	$ (9,716)	$ 14	$ 14	$ 17	$ 17	$ 5,469	$ 5,230	$ 5,469	$ 5,230