Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Narrative) (Loans) (Detail)	12 Months Ended
	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Minimum number of days to be considered past due	90 days
Threshold period past due for write-off of financing receivable (in days)	180 days
Days past due and still accruing (in days)	90 days
Minimum period for troubled debt restructurings placed on non accrual status (in months)	6 months
Minimum performance period for TDR to return to accrual status (in months)	6 months
Residential Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Minimum number of days to be considered past due	90 days
Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Minimum number of days to be considered past due	90 days
Other Real Estate Owned [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Threshold period past due for write-off of financing receivable (in days)	90 days