Nonqualified Benefit Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Contribution Plan
Defined Benefit Plan Disclosure [Line Items]
Nonqualified Defined Contribution Plan, Cost	$ 42,400,000	$ 41,200,000	$ 40,900,000
Nonqualified Plan | Unfunded Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Nonqualified Defined Contribution Plan, Cost	597,000	736,000	395,000
Supplemental Employee Retirement Plan | Unfunded Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments in nonqualified benefit plans	121,930,000	122,927,000
Supplemental Employee Retirement Plan | Unfunded Plan [Member] | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Investments in nonqualified benefit plans	73,838,000	77,388,000
Supplemental Employee Retirement Plan | Unfunded Plan [Member] | Life insurance carried on plan participants
Defined Benefit Plan Disclosure [Line Items]
Investments in nonqualified benefit plans	37,274,000	38,568,000
Supplemental Employee Retirement Plan | Unfunded Plan [Member] | Other Investments
Defined Benefit Plan Disclosure [Line Items]
Investments in nonqualified benefit plans	10,818,000	6,971,000
Supplemental Employee Retirement Plan | Nonqualified Plan | Unfunded Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	93,988,000	102,484,000
Accumulated benefit obligation	93,988,000	102,484,000
Service cost	185,000	289,000	493,000
Interest cost	3,157,000	3,494,000	3,742,000
Amortization of prior service credit	0	0	(80,000)
Recognized net actuarial loss	1,047,000	883,000	952,000
Curtailment gain	0	0	(3,292,000)
Net periodic benefit cost (credit)	$ 4,389,000	$ 4,666,000	$ 1,815,000
Benefit obligation discount rate	3.86%	3.20%
Net periodic benefit cost discount rate	3.20%	3.56%
Nonqualified Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	$ 7,350,000
Nonqualified Benefit Plan, Expected Future Benefit Payment, Year Two	7,766,000
Nonqualified Benefit Plan, Expected Future Benefit Payment, Year Three	7,787,000
Nonqualified Benefit Plan, Expected Future Benefit Payment, Year Four	7,018,000
Nonqualified Benefit Plan, Expected Future Benefit Payment, Year Five	7,213,000
Nonqualified Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter	$ 36,885,000