Loans and Allowance for Loan Losses (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment in impaired loans	$ 309,344,000	$ 537,540,000	$ 309,344,000	$ 537,540,000
Provision for loan losses	(2,956,000)	(3,843,000)	(13,990,000)	(25,638,000)
Interest income recognized	2,193,000		7,333,000	0	$ 14,861,000
Average recorded investment in impaired loans	323,486,000	559,700,000	375,471,000	666,800,000	622,046,000
Interest income recognized for accruing TDRs		3,700,000		11,700,000
Allowance for loan losses	250,900,000	269,376,000	$ 250,900,000	269,376,000	261,317,000	$ 254,702,000	$ 277,783,000	$ 307,560,000
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	240,400,000		$ 240,400,000		348,400,000
Allowance for loan losses	16,200,000		16,200,000		21,000,000
Minimum [Member] | Accruing TDRs With Modifications And Renewals Completed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial-type impaired loans			1,000,000
Unallocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment in impaired loans	0	0	0	0
Provision for loan losses	0	0	0	23,000,000
Allowance for loan losses	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 23,000,000