Off-Balance-Sheet Originate Loans and Letters of Credit (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Line Items]
Commitments	$ 2,543,065
Total loan commitments
Commitments and Contingencies Disclosure [Line Items]
Commitments	2,034,944	$ 1,900,000
Commercial, performance stand-by, and financial stand-by letters of credit
Commitments and Contingencies Disclosure [Line Items]
Commitments	508,121	$ 339,400
Total mortgage loan commitments
Commitments and Contingencies Disclosure [Line Items]
Commitments	608,734
Total mortgage loan commitments | Multi-family and commercial real estate
Commitments and Contingencies Disclosure [Line Items]
Commitments	365,788
Total mortgage loan commitments | One-to-four family
Commitments and Contingencies Disclosure [Line Items]
Commitments	1,478
Total mortgage loan commitments | Acquisition, development, and construction
Commitments and Contingencies Disclosure [Line Items]
Commitments	241,468
Other loan commitments
Commitments and Contingencies Disclosure [Line Items]
Commitments	$ 1,426,210