Covered Loans Acquired in Acquisitions of AmTrust Bank ("Am Trust") and Desert Hills (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered loans	$ 0	$ 1,698,133
Covered loans held for sale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered loans	$ 1,698,133
Percent of Covered Loans	100.00%
One-to-four family | Covered loans held for sale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered loans	$ 1,609,635
Percent of Covered Loans	94.80%
Other loans | Covered loans held for sale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered loans	$ 88,498
Percent of Covered Loans	5.20%