Fair Value (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Other noninterest-bearing investments valued under the cost method	$ 15,100		$ 15,100		$ 25,300
Federal Home Loan Bank Stock and Federal Reserve Bank Stock	221,300		221,300		191,500
Net gains on sale of OREO properties	137	$ 40	1,993	$ 111
Principal amount of other real estate owned property sold			8,400	13,100
OREO Properties [Member]
Derivatives, Fair Value [Line Items]
Net gains on sale of OREO properties	400	$ 800	3,200	$ 2,700
Fair Value, Inputs, Level 2 [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	10,319,101		10,319,101		7,581,309
Fair Value, Inputs, Level 3 [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	0		0		$ 0
Third Party Pricing Service [Member] | Fair Value, Inputs, Level 2 [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	$ 0		$ 0