Covered Loans Acquired in AmTrust and Desert Hills Acquisitions (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered loans	$ 2,149,055	$ 2,428,622
Percent of Covered Loans	100.00%
One-to-four family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered loans	$ 1,993,640
Percent of Covered Loans	92.80%
Other loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered loans	$ 155,415
Percent of Covered Loans	7.20%