Summary of Significant Accounting Policies (Loans Modified Under Troubled Debt Restructuring) (Details)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Number of minimum days when principal or interest is past due is placed in nonaccrual category	90 days
Time period of real estate residential troubled debt restructurings reducing borrower's monthly payments by decreasing the interest rate charged on the loan	24 months