Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income tax benefits due to ASU 2016-09		$ 4,775
Net tax benefit recognized from stock compensation plans			$ 1,055	$ 3,291
Income tax expense recorded after impact of Tax Act	$ 41,700
Remeasurements of certain deferred tax assets and liabilities, net	33,100
Tax credits and other tax benefits related to qualified affordable housing partnerships	$ 7,900
Other comprehensive income, available for sale securities, income tax benefit		$ (1,500)	$ (16,400)	$ (7,500)