Employee Benefit Plans (Narrative) (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) participant financial_institution yr plan shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of 401(k) plans administered | plan	1
Minimum employee age required to participate in the plan (in years) | yr	21
Expense for the company plan contributions	$ 3,100,000	$ 3,200,000	$ 2,600,000
Expense with deferred compensation plan	236,200	181,100	128,500
Accrued liabilities with deferred compensation plan	$ 5,500	$ 5,500	80,200
Number of supplemental executive retirement plans | plan	2
Unallocated shares | shares	79,548	109,950
Unallocated shares, aggregate cost	$ 433,000	$ 599,000
ESOP shares committed to be released	$ 458,000	$ 543,000	$ 501,000
Granted (in shares) | shares	0	0	0
401(k) plan 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Company contribution as percentage of compensation of eligible employees	5.00%
Health Insurance Postretirement Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Aggregate benefits payable included in accrued expenses and other liabilities	$ 1,800,000	$ 1,500,000	$ 1,500,000
Discount rate used to determine the actuarial present value of projected postretirement benefit obligations (as a percent)	3.19%	4.22%	3.62%
Estimated prior service credit that will be amortized from accumulated other comprehensive income into net periodic benefit cost	$ 100,000
Assumed health care trend rates used in 2019 through 2023, high end of range (as a percent)	5.90%
Assumed health care trend rates used in 2019 through 2023, low end of range (as a percent)	5.10%
Ultimate health care trend rate after 2020 (as a percent)	4.50%
Expenses for benefits payable recognized under agreement	$ 66,000	$ 108,000	$ 24,000
Supplemental retirement plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Aggregate benefits payable included in accrued expenses and other liabilities	$ 12,800,000	12,100,000
Number of participants | participant	13
Expenses for benefits payable recognized under agreement	$ 1,100,000	$ 500,000
Discount rate used to determine the actuarial present value (as a percent)	3.25%	4.00%
Below age 65 | Health Insurance Postretirement Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual health care trend that will be used to measure the accumulated postretirement benefit obligation (as a percent)	13.30%
Actual health care trend used to measure the accumulated postretirement benefit obligation (as a percent)		3.10%
Over age 65 | Health Insurance Postretirement Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual health care trend that will be used to measure the accumulated postretirement benefit obligation (as a percent)	1.20%
Actual health care trend used to measure the accumulated postretirement benefit obligation (as a percent)		2.40%
Employee Stock Ownership Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
ESOP loan to purchase shares of entity's common stock | shares	546,986
Number of years during which quarterly installments are payable	30 years
Percentage of interest payable per annum on loan obtained by the ESOP	8.50%
Outstanding balance of loan	$ 800,000	$ 1,000,000.0
Unallocated shares | shares	79,548	109,950
Unallocated shares, aggregate cost	$ 400,000	$ 600,000
Unallocated shares, market value	1,300,000	$ 1,500,000
ESOP shares committed to be released	$ 500,000
Number of shares committed to be released to eligible employees | shares	30,402	32,382	34,356
2011 Restricted Stock Award Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of authorized shares | shares	500,000
Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of authorized shares | shares	1,750,000
Share-based compensation expense	$ 2,400,000	$ 2,500,000	$ 2,300,000
Tax benefits from vested awards	$ 100,000	1,200,000	700,000
Performance-based shares
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of financial institutions comprising peer group | financial_institution	17
Restricted stock
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Dividends paid on unvested shares recognized as compensation expense	$ 100,000	200,000	100,000
Stock Options
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Share-based compensation expense	$ 0	0	0
Exercisable period upon happening of a specific event, low end of range (in months)	3 months
Exercisable period upon happening of a specific event, high end of range (in years)	5 years
Dividend equivalent rights	$ 0	$ 0	$ 0
Vesting equally over three years | Time-based shares
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percent of shares in tranche	50.00%
Award vesting period	3 years
Vesting percentage	33.00%
Vesting after achievement of performance targets | Performance-based shares
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percent of shares in tranche	50.00%
Award vesting period	3 years