Investments (Narrative) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($) investments	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) investments	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Investments [Abstract]
Securities gains (losses)	$ 12,529,000	$ 147,000	$ 17,157,000	$ 5,273,000
Unrealized Losses Related to Marketability of Securities or Issuer's Ability to Honor Redemption Obligations	0		0		$ 0
Fair Value, 12 months or more in unrealized loss position	197,332,000		197,332,000		280,126,000
Unrealized Losses, Greater than 12 months	$ 1,039,000		$ 1,039,000		6,094,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | investments	36		36
Investment value deemed to be OTTI	$ 0		$ 0
Investment securities, aggregate carrying value, pledged as collateral	$ 4,770,000,000		$ 4,770,000,000		$ 4,730,000,000