Investment Securities Summary of Gains and Losses from Equity and Debt Securities, and Losses from Other-than-Temporary Impairment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Gross Realized Gains	$ 13,873	$ 2,586	$ 9,067
Gross Realized Losses	(4,802)	(36)	(1)
Net Gains (Losses)	9,071	2,550	9,066
Equity securities
Gross Realized Gains	13,558	2,005	6,496
Gross Realized Losses	0	(10)	(1)
Net Gains (Losses)	13,558	1,995	6,495
Debt securities
Gross Realized Gains	315	581	2,571
Gross Realized Losses	(4,802)	(26)	0
Net Gains (Losses)	$ (4,487)	$ 555	$ 2,571