Acquisitions - Summary of Financial Statement Captions Impacted by Recast Adjustments (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Jun. 30, 2014
Recast Adjustment [Line Items]
Purchased loans	$ 1,826,848		$ 1,147,947	$ 1,404,069
Net deferred tax asset	96,973		$ 79,176	$ 81,553
Intervest Bancshares Corporation [Member]
Recast Adjustment [Line Items]
Goodwill	$ 44,200
As Previously Reported [Member] | Intervest Bancshares Corporation [Member]
Recast Adjustment [Line Items]
Purchased loans		$ 2,042,164
Net deferred tax asset		63,483
Goodwill		125,603
Income taxes receivable		689
Recast Adjustment [Member] | Intervest Bancshares Corporation [Member]
Recast Adjustment [Line Items]
Purchased loans		4,393
Net deferred tax asset		(985)
Goodwill		(2,719)
Income taxes receivable		(689)
As Recast [Member] | Intervest Bancshares Corporation [Member]
Recast Adjustment [Line Items]
Purchased loans		2,046,557
Net deferred tax asset		62,498
Goodwill		122,884
Income taxes receivable		$ 0