Fair Value Fair Value (Impaired Financing Receivables Additional Information) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Schedule of Impaired Financing Receivables Additional Information [Line Items]
Book Value Of Impaired Loans Carried At Fair Value	$ 3,908	$ 3,577
Partial Charge-Offs On Impaired Loans carried at Fair Value	2,734	2,780
Impaired Financing Receivable, Related Allowance	1,207	684
impaired Financing Receivable, loans not held at Fair Value, Carrying Amount	45,248	52,306
Impaired Financing Receivable, Recorded Investment	50,322	56,564	$ 70,127
Impaired Loan Fair Value	3,867	3,574
Impaired Financing Receivable, loans not held at Fair Value, Recorded Investment	46,414	52,987
Partial Charge-offs on Impaired Loans carried at Cost	7,238	7,260
Impaired Financing Receivable, Carrying Value	49,115	55,880
Partial Charge-Offs On Impaired Loans	9,972	10,040
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,207	684
Financing Receivable, not collateral dependent [Domain]
Schedule of Impaired Financing Receivables Additional Information [Line Items]
Impaired Financing Receivable, Related Allowance	1,166	681
Commercial Receivables, excluding Commercial, Financial, and Agricultural [Domain]
Schedule of Impaired Financing Receivables Additional Information [Line Items]
Impaired Financing Receivable, Related Allowance	$ 41	$ 3