Guarantees (Changes in liabilty of estimated loss from credit recourse agreement) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement In Guaranteed Benefit Liability Gross Roll Forward
Balance at beginning of the period	$ 710	$ 439	$ 927
Net charge-off/terminations	(352)	(271)	(488)
Balance at the end of the period	$ 358	$ 710	$ 439