Significant Accounting Policies Cash Equivalents (Details)	12 Months Ended
	Dec. 31, 2018
Cash and Cash Equivalents [Abstract]
Maturity of Federal Funds Sold Considered Cash Equivalents	1 day
Maturity of Resell Agreement Considered Cash Equivalents, Minimum	1 day
Maturity of Resell Agreements Considered Cash Equivalents, Maximum	30 days