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Loans and Allowance for Credit Losses Allowance for Credit Losses (Details) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Mar. 31, 2017
Dec. 31, 2016
Receivables [Abstract]        
Allowance for loan losses $ 163,217 $ 169,910 $ 170,076 $ 168,679
Reserve for unfunded lending commitments 12,802 6,174    
Allowance for credit losses $ 176,019 $ 176,084 $ 172,647 $ 171,325