Fair Value (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Other noninterest-bearing investments valued under the cost method	$ 28,700		$ 28,700		$ 39,100
Federal Home Loan Bank Stock and Federal Reserve Bank Stock	220,200		220,200		250,700
Net gains on sale of OREO properties	40	$ (875)	111	$ (2,216)
Principal amount of other real estate owned property sold			13,100	30,700
OREO Properties [Member]
Derivatives, Fair Value [Line Items]
Net gains on sale of OREO properties	800	$ 1,900	2,700	4,400
Impairment of OREO properties			(400)	$ (500)
Level 2 [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	5,981,502		5,981,502		3,336,943
Level 3 [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	0		0		$ 401,957
Third Party Pricing Service [Member] | Level 2 [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	$ 0		$ 0
Trust Preferred Predominantly Banks [Member] | Minimum [Member]
Derivatives, Fair Value [Line Items]
Significant Unobservable Inputs, Loss Given Deferral Rate			11.90%		14.50%
Discount Rate Range Of Libor Utilized For Fair Value Purposes			3.70%		3.40%
Trust Preferred Predominantly Banks [Member] | Maximum [Member]
Derivatives, Fair Value [Line Items]
Significant Unobservable Inputs, Loss Given Deferral Rate			100.00%		100.00%
Discount Rate Range Of Libor Utilized For Fair Value Purposes			5.40%		5.60%
Constant Prepayment Rate Until Maturity [Member] | Trust Preferred Predominantly Banks [Member]
Derivatives, Fair Value [Line Items]
Assumption for Fair Value of Assets or Liabilities that relate to Transferor's Continuing Involvement, Prepayment Speed			2.00%		2.00%