Pension and Other Post-Retirement Benefit Plans (Fair Value of Plan Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Hedge funds and private equity [Member] | Measured at net asset value [Domain]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 2,083	$ 4,599
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	746,763	625,646	$ 681,573
Defined Benefit Plan Assets fair value hierarchy	744,680	621,047
Pension Plans [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	74,263	63,852
Pension Plans [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	670,417	557,195
Pension Plans [Member] | Measured at net asset value [Domain]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	2,083	4,599
Pension Plans [Member] | Common trust funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	3,467	3,961
Pension Plans [Member] | Common trust funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Pension Plans [Member] | Common trust funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	3,467	3,961
Pension Plans [Member] | Corporate stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	14,995	13,142
Pension Plans [Member] | Corporate stock [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	14,553	13,142
Pension Plans [Member] | Corporate stock [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	442	0
Pension Plans [Member] | Mutual funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	176,777	139,730
Pension Plans [Member] | Mutual funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	59,710	48,645
Pension Plans [Member] | Mutual funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	117,067	91,085
Pension Plans [Member] | Fixed income investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	549,441	464,214
Pension Plans [Member] | Fixed income investments [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	2,065
Pension Plans [Member] | Fixed income investments [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 549,441	$ 462,149