Investment Securities (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) security	Dec. 31, 2016 USD ($) security	Dec. 31, 2015 USD ($)
Investment Securities [Abstract]
Securities pledged as collateral	$ 838,400	$ 907,700
Number of security positions, unrealized loss position | security	411	463
Number of security positions, unrealized loss position for more than 12 months | security	172	9
Securities, 12 months or longer, Fair Value	$ 274,763	$ 5,526
Securities, 12 months or longer, Unrealized Losses	$ 7,033	$ 19
Number of security positions, unrealized loss position for less than 12 months | security	239	454
Securities, less than 12 months, Fair Value	$ 433,097	$ 642,858
Securities, less than 12 months, Unrealized Losses	3,957	12,609
OTTI charge recognized	$ 0	$ 0	$ 0