Loans and Allowance for Credit Losses Loans Modified Under Troubled Debt Restructurings (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Modifications [Line Items]
Total Accruing Troubled Debt Restructurings	$ 71,614	$ 66,379
Non-accrual TDRs (1)	24,897	29,051
Total TDRs	96,511	95,430
Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Total Accruing Troubled Debt Restructurings	25,602	26,016
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Total Accruing Troubled Debt Restructurings	18,181	13,959
Real-estate - home equity
Financing Receivable, Modifications [Line Items]
Total Accruing Troubled Debt Restructurings	16,067	15,558
Commercial
Financing Receivable, Modifications [Line Items]
Total Accruing Troubled Debt Restructurings	11,740	10,820
Consumer
Financing Receivable, Modifications [Line Items]
Total Accruing Troubled Debt Restructurings	$ 24	$ 26