Employee Benefit Plan (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2030
Defined Benefit Plan Disclosure [Line Items]
Transfers between Level 1 and Level 2	$ 0
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated transition obligation amortized from accumulated other comprehensive income into net public benefit cost over the next year	0
Estimated actuarial loss amortized from accumulated other comprehensive income into net periodic benefit cost over the next year	7,709,000
Estimated prior service cost amortized from accumulated other comprehensive income into net periodic benefit cost over the next year	$ 0
Weighted average discount rate used to determine net periodic benefit cost	3.28%	4.27%	3.62%
Rate of compensation increase to determine the net periodic benefit cost	4.00%	4.00%	4.00%
Expected long-term rate of return on plan assets	7.00%	7.00%	7.00%
Weighted average discount rates used to determine actuarial present value of the projected benefit obligation	2.55%	3.28%	4.27%
Company contributions	$ 6,825,000	$ 4,750,000	$ 77,743,000
Transfers between Level 1 and Level 2	0
Plan assets	354,464,000	301,467,000	260,531,000
Defined Benefit Pension Plans [Member] | Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Private equity limited partnership	4,596,000	20,351,000
Company contributions	$ 0	0
Defined Contribution Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plans, employer contribution plans, employer contribution percentage, maximum	3.00%
Defined contribution plans, employer contribution percentage, for new hires, minimum	3.00%
Defined contribution plans, employer contribution percentage, for new hires, maximum	8.00%
Vested contribution after three years, percentage	100.00%
Defined contribution plans vesting period, years	3 years
Defined contribution plan employer contribution percentage for branch offices, minimum	7.90%
Defined contribution plan employer contribution percentage for branch offices, maximum	8.80%
Post-Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated transition obligation amortized from accumulated other comprehensive income into net public benefit cost over the next year	$ 0
Estimated actuarial loss amortized from accumulated other comprehensive income into net periodic benefit cost over the next year	46,000
Estimated prior service cost amortized from accumulated other comprehensive income into net periodic benefit cost over the next year	$ (577,000)	$ (577,000)	$ (577,000)
Weighted average discount rate used to determine net periodic benefit cost	3.28%	4.27%	3.62%
Weighted average discount rates used to determine actuarial present value of the projected benefit obligation	2.55%	3.28%	4.27%
Company contributions	$ 232,000	$ 488,000
Health inflation rate	6.75%
Plan assets
Post-Retirement Plan [Member] | Scenario Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Health inflation rate				4.75%
Equity Securities [Member] | Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets consist of shares in investment trusts, percentage	72.00%
Target asset allocation percentage	70.00%
Fixed Maturities [Member] | Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets consist of shares in investment trusts, percentage	27.00%
Limited Partner [Member] | Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets consist of shares in investment trusts, percentage	1.00%
Cash [Member] | Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets consist of shares in investment trusts, percentage	0.00%
Bonds [Member] | Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation percentage	30.00%