Investment Securities (Other-than-temporarily Impaired Securities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Than Temporary Impairment Credit Losses Recognized In Earnings Roll Forward
Begging Balance	$ 0	$ 1,490	$ 0
Realized from Securities Sold during the period	0	1,490	0
Additions from credit losses recognized on available-for-sale securities that had no previous impairment losses	0	0	1,490
Ending Balance	$ 0	$ 0	$ 1,490