Pension and Other Post-Retirement Benefit Plans (Fair Value of Plan Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Hedge funds and private equity [Member] | Measured at net asset value [Domain]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 4,599		$ 27,197
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	625,646	$ 681,573	$ 715,885
Defined Benefit Plan Assets fair value hierarchy	621,047	654,376
Pension Plans [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	63,852	74,678
Pension Plans [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	557,195	579,698
Pension Plans [Member] | Measured at net asset value [Domain]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	4,599	27,197
Pension Plans [Member] | Common trust funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	3,961	3,792
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	3,961	3,792
Pension Plans [Member] | Corporate stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	13,142	17,361
Pension Plans [Member] | Corporate stock [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	13,142	17,361
Pension Plans [Member] | Corporate stock [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Pension Plans [Member] | Mutual funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	139,730	166,817
Pension Plans [Member] | Mutual funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	48,645	53,391
Pension Plans [Member] | Mutual funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	91,085	113,426
Pension Plans [Member] | Fixed income investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	464,214	466,406
Pension Plans [Member] | Fixed income investments [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	2,065	3,926
Pension Plans [Member] | Fixed income investments [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 462,149	$ 462,480