Revenue Recognition, Noninterest Income by Major Source (Parenthetical) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disaggregation Of Revenue [Line Items]
Balance	$ 60,007,000	$ 56,142,000	$ 54,451,000	$ 52,633,000
Other service charges, commissions and other income	325,000	299,000	367,000
Income within the scope of ASC 606
Disaggregation Of Revenue [Line Items]
Other service charges, commissions and other income	$ 301,000	$ 269,000	$ 258,000