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Mortgage Servicing Rights - Additional Information (Detail) - USD ($)
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]      
Mortgage servicing rights $ 234,306,000   $ 233,961,000
Mortgage Banking Income      
Finite-Lived Intangible Assets [Line Items]      
Contractually specified servicing fees, late fees, and ancillary fees earned in exchange for servicing financial assets 311,000 $ 310,000  
Mortgage Receivable      
Finite-Lived Intangible Assets [Line Items]      
Unpaid principal balance of loans serviced for others 25,200,000,000   $ 25,100,000,000
Impairment of intangible assets $ 0 $ 0