Loans and Allowance for Loan Losses (Narrative) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment in impaired loans	$ 235,553,000	$ 298,600,000	$ 274,515,000
Interest income recognized	1,689,000	0	8,196,000
Interest income recognized for accruing TDRs		2,000,000
Non-accrual status	62,300,000		53,700,000
Provision for loan losses	8,674,000	9,377,000
Allowance for loan losses	253,514,000	$ 254,516,000	251,758,000	$ 252,496,000
Accruing TDRs With Modifications And Renewals Completed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing troubled debt restructuring	172,400,000
Provision for loan losses	$ 8,600,000		9,800,000
Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retail loan substandard period (in days)	90 days
Loss And Charged Off [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retail loans downgraded to loss (in days)	120 days
Accruing TDRs With Modifications And Renewals Completed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing troubled debt restructuring			$ 195,800,000
Accruing TDRs With Modifications And Renewals Completed [Member] | Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial-type impaired loans	$ 1,000,000