Employee Benefits (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended			120 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 30, 2023
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution amounts	$ 2,300	$ 2,300	$ 1,800
Other incentive-based compensation expense	16,900	16,000	$ 14,300
Deferred compensation plan, accrued liability	$ 14,200	10,800
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution	3.00%
Qualified Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Funded (unfunded) status at end of period	$ 6,641	2,836
Accumulated benefit obligation	72,900	65,800
Estimated amortization of prior service cost (credit) from accumulated other comprehensive loss into net period benefit cost, next year	(23)
Estimated amortization of (gain) loss from accumulated other comprehensive loss into net period benefit cost, next year	$ 1,500
Fair value of equity securities, maximum percentage held by a single issuer	10.00%
Estimated future employer contributions in next fiscal year	$ 3,000
Qualified Pension Plan [Member] | Equity Securities [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	50.00%
Qualified Pension Plan [Member] | Equity Securities [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	70.00%
Qualified Pension Plan [Member] | Small-Cap Equity Securities [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	20.00%
Qualified Pension Plan [Member] | Mid-Cap Equity Securities [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	20.00%
Qualified Pension Plan [Member] | International Equity Securities [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	30.00%
Qualified Pension Plan [Member] | Fixed Income Securities [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	30.00%
Qualified Pension Plan [Member] | Fixed Income Securities [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	50.00%
Qualified Pension Plan [Member] | Cash and Cash Equivalents [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%
Qualified Pension Plan [Member] | Cash and Cash Equivalents [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	10.00%
Qualified Pension Plan [Member] | High Yield Bond [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	10.00%
Non-Qualified Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Available-for-sale securities and other short-term investments, rabbi trusts	$ 13,300	11,700
Funded (unfunded) status at end of period	(15,203)	(13,154)
Accumulated benefit obligation	14,000	$ 12,000
Estimated amortization of prior service cost (credit) from accumulated other comprehensive loss into net period benefit cost, next year	(1)
Estimated amortization of (gain) loss from accumulated other comprehensive loss into net period benefit cost, next year	287
Estimated future employer contributions in next fiscal year	$ 897
Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Transition Period Pension Plan Amendment				10 years
Non-elective Employer Contribution [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution	4.00%