Comprehensive Income and Accumulated Other Comprehensive Income - Reclassification Out of Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	$ 19,348	$ 12,447	$ 49,813	$ 34,174
Income tax expense	(5,869)	(2,748)	(13,012)	(7,980)
Net income	13,479	9,699	36,801	26,194
Changes in net unrealized gains on investment securities [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Unrealized gains/(losses) on available for sale securities	1	(484)	(270)	362
Other-than-temporary impairment	5	(190)	(8)	(607)
Income before income taxes	6	(674)	(278)	(245)
Income tax expense	(2)	236	97	86
Net income	$ 4	$ (438)	$ (181)	$ (159)