Covered Loans Acquired in Acquisitions of AmTrust Bank ("Am Trust") and Desert Hills (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Jul. 28, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Covered loans	$ 0	$ 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%