Retirement Plans (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Contributions by Employer	$ 4,000
Composite market value factor, minimum range	0.995927	1.018148
Composite market value factor, maximum range	1.049539	1.081039
Fair Value Level Transfers Among Levels 1, 2, and 3	0	0
Owner Occupied And Commercial Real Estate Loans Unamortized Premiums	$ 19,900	$ 26,200
Benefit liability other supplement retirement plans	$ 6,400	6,900
Shares of company common stock | shares	233,849
Dividends received under the plan	$ 65	56
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	$ 26,100	25,500	$ 24,300
Minimum range of eligible compensation for noncontributory profit sharing feature	0.00%
Maximum range of eligible compensation for noncontributory profit sharing feature	6.00%
Accrued profit sharing expense	$ 6,300	$ 6,100	$ 12,000
Contribution rate of profit sharing expenses	0.01		0.02
Composite market value factor, at end of period	1.042254	1.063133
Limited Partnerships, Capital Commitment	$ 8,750
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target investment allocation percentage in equity	65.00%
Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target investment allocation percentage in equity	30.00%
Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Target investment allocation percentage in equity	5.00%
Limited Liability Partnerships [Member]
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]
Defined Benefit Plan, Fair Value of Plan Assets	$ 5,100	$ 6,200