Retirement Plans (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Benefit liability other supplement retirement plans	$ 5,000	$ 6,400
Shares of company common stock | shares	233,849
Rate of employee contribution from earnings	80.00%
Matching contribution allocation rate first time	100.00%
Employee contribution rate for first time matching	3.00%
Matching contribution allocation rate second time	50.00%
Employees contribution rate for second time matching	2.00%
Employer contribution in common stock	$ 29,000	26,400	$ 26,100
Minimum range of eligible compensation for noncontributory profit sharing feature	0.00%
Maximum range of eligible compensation for noncontributory profit sharing feature	4.00%
Accrued profit sharing expense	$ 17,000	$ 11,000	$ 6,000
Contribution rate of profit sharing expenses	0.0250	0.0175	0.0100
Limited Partnerships, Capital Commitment	$ 9,000
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target investment allocation percentage in equity	9.00%
Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target investment allocation percentage in equity	88.00%
Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Target investment allocation percentage in equity	3.00%
Limited Liability Partnerships [Member]
Defined Benefit Plan [Abstract]
Defined Benefit Plan, Plan Assets, Amount	$ 4,000	$ 4,000
Common Stock [Member]
Defined Benefit Plan [Abstract]
Defined Benefit Plan, Plan Assets, Amount	10,000	12,000
Common Stock [Member] | Insurance Company Pooled Separate Accounts [Member]
Defined Benefit Plan [Abstract]
Defined Benefit Plan, Plan Assets, Amount	15,000	97,000
Debt [Member] | Insurance Company Pooled Separate Accounts [Member]
Defined Benefit Plan [Abstract]
Defined Benefit Plan, Plan Assets, Amount	$ 116,000	31,000
Real Estate Investment [Member] | Insurance Company Pooled Separate Accounts [Member]
Defined Benefit Plan [Abstract]
Defined Benefit Plan, Plan Assets, Amount		$ 8,000