Investments (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) investments	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) investments	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Investments [Abstract]
Securities gains (losses)	$ 352,000	$ 5,564,000	$ 17,509,000	$ 10,837,000
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	289,161,000		289,161,000		280,126,000
Unrealized Losses, Greater than 12 months	$ 2,172,000		$ 2,172,000		6,094,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | investments	40		40
Investment value deemed to be OTTI	$ 0		$ 0
Investment securities, aggregate carrying value, pledged as collateral	$ 4,670,000,000		$ 4,670,000,000		$ 4,730,000,000