Employee Benefit Plans (Narrative) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 28, 2017
Defined Benefit Plan Disclosure [Line Items]
Employee Stock Ownership Plan (ESOP), cash contributions to ESOP		$ 242,000	$ 99,000	$ 129,000
Employee Stock Ownership Plan (ESOP), number of allocated shares		223,344	221,106
Employee Stock Ownership Plan (ESOP), number of unallocated shares		22,908	9,562
Employee Stock Ownership Plan (ESOP), allocated shares market value		$ 9,400,000	$ 6,700,000
Employee Stock Ownership Plan (ESOP), allocated excess of fair market value of leveraged ESOP shares released		$ 110,000
Share Price					$ 38.78
Employee Stock Ownership Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employee Stock Ownership Plan (ESOP) promissory note amortization period		7 years
Employee Stock Ownership Plan (ESOP), debt structure offset by purchase of common shares, amount	$ 823,000
Promissory notes		$ 755,000	$ 169,000
Employee Stock Ownership Plan (ESOP), Debt Structure, Direct Loan, Employer Cash Payments Used for Debt Service		$ 237,000
Employee Stock Ownership Plan (ESOP), debt structure direct loan employer shares used for debt service, Shares		10,157
Employee Stock Ownership Plan (ESOP), debt structure offset by purchase of common shares	23,503
Share Price		$ 38.30	$ 29.00
Prime Rate [Member] | Employee Stock Ownership Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employee Stock Ownership Plan (ESOP) basis spread on variable rate		1.00%
401 (K) Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Retirement plan expense		$ 298,000	$ 346,000	332,000
Individual Supplemental Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Retirement plan expense		$ 637,000	525,000	519,000
Number of years following retirement benefit is paid		15 years
Nonqualified Retirement Plan For Non Employee Directors [Member]
Defined Benefit Plan Disclosure [Line Items]
Employee benefit plan requisite service period		15 years
Employee benefit plan vesting period		2 years
Retirement plan expense		$ 29,000	$ 20,000	$ 22,000
Maximum annual benefit following retirement		$ 3,500
Number of years following retirement benefit is paid		10 years